Film responsive to bicarbonate ion

ABSTRACT

A memberane sensitive to anions is obtained by forming into a membrane either a composition comprising an onium salt compound such as trioctylmethylammonium chloride or tetraoctylammonium bromide, and an aromatic boric diester compound such as (p-alkyloxy)phenyl borate, or a composition which comprises these two ingredients and a membrane-forming polymer such as polyvinyl chloride or polystyrene, and may further contain a fat-soluble anion salt such as tetraphenyl borate. This membrane can yield an ion-selective electrode which permits hydrogencarbonate ions contained in body fluids to be rapidly determined with high sensitivity and high selectivity and which has a long life.

TECHNICAL FIELD

This invention relates to a bicarbonate ion-sensitive membrane which isuseful in the construction of an ion-selective electrode for measuringthe activity of bicarbonate ion in a solution. More particularly, thisinvention relates to an anion-sensitive membrane which contains anaromatic boric diester structural unit and an onium salt structural unitand which, when it is used as the boundary membrane of an ion-selectiveelectrode, can detect bicarbonate ions (i.e., hydrogencarbonate ions)selectively.

BACKGROUND ART

In recent years, attempts are being extensively made to applyion-selective electrodes to medical fields and thereby determine variousions contained in biological fluids such as blood and urine. Its purposeis to measure the concentrations of specific ions in biological fluidsand thereby diagnose various diseases, on the basis of the fact thatsuch ion concentrations are closely related with metabolic reactions inthe living body. At present, ion-selective electrodes are being used tomeasure the concentrations of sodium ion, potassium ion and chloride ionin biological fluids, so that these ion concentrations can be measuredconveniently and rapidly.

Generally, as illustrated in FIG. 1, an ion-selective electrode isbasically constructed by providing a cylindrical vessel 11 with abarrier membrane comprising an anion-sensitive membrane 12 at the partthereof which is to be immersed in sample solutions (generally at thebottom thereof) and placing therein an internal electrolyte 13 and aninternal reference electrode 14.

FIG. 2 illustrates a typical construction of an ion measuring apparatusfor measuring the activity of an ion in a solution by using such anion-selective electrode. Specifically, an ion-selective electrode 21,together with a salt bridge 22, is immersed in a sample solution 23. Theother end of the salt bridge, together with an external reference 24, isimmersed in a saturated potassium chloride solution 26. The potentialdifference between both electrodes is read with an electrometer 25, andthe ionic activity of a specific ionic species in the sample solutioncan be determined from the potential difference. The performance of theion-selective electrode used in such an ion measuring apparatus isgreatly affected by the performance of the ion-sensitive membrane usedtherein.

Hydrogencarbonate ion is one of the important ions present in biologicalfluids, particularly blood. Since hydrogencarbonate ion is an importantfactor in revealing the state of respiratory and metabolic functions inthe living body, information useful for the diagnosis of variousdiseases such as diabetes mellitus and renal disorders can be obtainedby the measurement of Hydrogencarbonate ion. At present,hydrogencarbonate ion concentrations are calculated from the pH of thesample and the measured value of carbon dioxide partial pressure(P_(CO2)) according to the following equation.

pH=6.1+log{[HCO₃ ⁻]/0.03·PCO₂}

This method requires a measuring time of as long as about 30 to 60seconds. Moreover, it is necessary to employ a measuring methoddifferent from that for the aforesaid sodium ion-, potassium ion- andchloride ion-selective electrodes. Consequently, it is necessary tomeasure hydrogencarbonate ion concentrations in a system different fromthat for the measurement of sodium and potassium ion concentrations.

Generally, ion-selective electrodes can reduce the time required formeasurement to the order of several seconds. Moreover, theconcentrations of various ions can be simultaneously measured by using acombination of ion-selective electrodes corresponding to ionic speciesto be measured. Owing to these advantages, a variety of anion-sensitivemembranes for the selective detection of hydrogen-carbonate ion haveconventionally been proposed. They include, for example,

(a) a membrane obtained by mixing a polymer (e.g., polyvinyl chloride)with a fat-soluble cation salt (e.g, a quaternary ammonium salt), atrifluoroacetophenone derivative (e.g., trifluoro-acetyl-p-alkylbenzene)and a plasticizer, and forming this mixture into a membrane; and

(b) a membrane obtained by mixing a polymer (e.g., polyvinyl chloride)with an organotin compound (e.g., trioctyltin chloride) and aplasticizer and optionally with a trifluoroacetophenone derivative(e.g., trifluoroacetyl-p-alkylbenzene), and forming this mixture into amembrane.

Ion-selective electrodes using the anion-sensitive membrane of theaforesaid type (a) include, for example, an electrode disclosed by Wiseet al. (U.S. Pat. No. 3,723,281), an electrode reported by Greenberg etal. [J. Greenberg et al., Anal. Chim. Acta, 141: p. 57-64 (1982)], anelectrode disclosed by Chapoteau et al. (Japanese Laid-Open Patent No.10759/'86=EP-A-155162), and an electrode disclosed by Yamaguchi et al.(Japanese Laid-Open Patent No. 265559/'87=EP-A-245168).

Moreover, ion-selective electrodes using the anion-sensitive membrane ofthe aforesaid type (b) include an electrode reported by Oesch et al. [J.Oesch et al., J. Chem. Soc. Faraday Trans. 1, 82: p. 1179-1186 (1986)],an electrode disclosed by Ushizawa et al. (Japanese Laid-Open Patent No.204368/'92), and the like.

However, the ion-selective electrodes using the anion-sensitive membraneof the aforesaid type (a) are known to have poor selectivity relative tofat-soluble ions such as nitrate and thiocyanate ions. Moreover, theyalso have the disadvantage that their electric potential response isrelatively slow (about 1 minute) and their lives are short because theion-sensitive substance present in the membrane gradually dissolves inthe solution.

On the other hand, the ion-selective electrodes using theanion-sensitive membrane of the aforesaid type (b) are known to havepoor selectivity relative to chloride ion, because an organotin compoundis contained in the membrane. Moreover, they also have the disadvantagethat their lives are short because the ion-sensitive substance presentin the membrane gradually dissolves in the solution.

Accordingly, it is desired to develop an anion-sensitive membranecapable of yielding an ion-selective electrode which permitshydrogencarbonate ions contained in biological fluids to be rapidlydetermined with high selectivity and which has a long life.

The present inventors have carried out intensive investigations with aview to developing an anion-sensitive membrane which can solve theabove-described problems. As a result, it has now been found that, whena polymer membrane formed by using an onium salt compound and an organicboric diester compound is used as an anion-sensitive membrane,hydrogencarbonate ions present in a solution can be rapidly determinedwith high selectivity and, moreover, the membrane has a long life. Thepresent invention has been completed on the basis of this finding.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a membranesensitive to bicarbonate ion comprising a polymer membrane whichcontains an onium salt structural unit (A) and an aromatic boric diesterstructural unit (B) of the formula

 

wherein Ar is an aromatic carbocyclic group which may optionally haveone or more substituents, either in the form of low-molecular-weightcompounds dispersed in the polymer or in a form introduced into apolymer molecule.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an ion-selective electrode using ananion-sensitive membrane; and

FIG. 2 is a schematic view of an apparatus for measuring an electricpotential difference by using an ion-selective electrode.

The bicarbonate ion-sensitive membrane of the present invention will bemore specifically described hereinbelow.

EMBODIMENTS OF THE INVENTION

A polymer membrane in accordance with the present invention contains:.

(1) an onium salt structural unit (A), and

(2) an aromatic boric diester structural unit (B) of the formula

 

 wherein Ar is an aromatic carbocyclic group which may optionally haveone or more substituents. In the polymer membrane, these structuralunits (A) and (B) may be present in any suitable form. For example, eachof the structural units (A) and (B) may take the form of alow-molecular-weight compounds dispersed in a polymer matrix, or atleast one of the structural units (A) and (B) may be present in a formintroduced into a polymer molecule. Where any one of the structuralunits (A) and (B) is present in a form introduced into a polymermolecule, the polymer containing this structural unit may be used as atleast a part of the aforesaid polymer matrix.

Now, the onium salt structural unit (A) and the aromatic boric diesterstructural unit (B) are described below.

Onium Salt Structural Unit (A)

In the polymer membrane in accordance with the present invention, theonium salt structural unit (A) may be present in the form of alow-molecular-weight compound or in a form introduced into a polymermolecule. In this description, the onium salt structural units in bothforms are collectively referred to as “onium salt compounds”.

Onium salt compounds are compounds in which cation type atomic groupsare coordinated to an atom having a lone pair, such as a nitrogen,phosphorus, sulfur, oxygen or arsenic atom. In the present invention,any well-known onium salt compound may be used. The onium salt compoundswhich can preferably be used in the present invention include, forexample, quaternary ammonium salts, pyridinium salts, phosphonium salts,sulfonium salts, oxonium salts and arsonium salts.

As the onium salt compound becomes less soluble in sample solutions tobe measured, the bicarbonate ion-sensitive membrane of the presentinvention can provide a longer electrode life. Accordingly, it ispreferable that the solubility of the onium salt compound in water whichis commonly used for sample solutions to be measured be not greater than0.001. The term “solubility” as used herein refers to the maximum weight(g/dl) of the solute in a saturated solution at 20° C.

The onium salt compounds are more fully explained below. First of all,typical onium salt compounds are quaternary ammonium salts representedby the following formula (1):

 

wherein R¹ to R⁴ are each independently a hydrogen atom or an organicgroup, and A⁻ is an anion. Compounds formed by the addition of ahydrogen ion to a primary, secondary or tertiary amine so as to producea positive charge can also be used as quaternary ammonium salts.

In the above formula (1), no particular limitation is placed on the typeof the organic groups. However, useful organic groups generally includehydrocarbon radicals such as aliphatic hydrocarbon radicals, aromatichydrocarbon radicals and alicyclic hydrocarbon radicals; heterocyclicgroups; groups formed by the attachment of —O—, —CO—, —COO—, —CONH—,—CON<, —N═CH— or the like to an end of such a hydrocarbon radical orheterocyclic group; groups formed by joining two such hydrocarbonradicals, two such heterocyclic groups, or such a hydrocarbon radicaland such a heterocyclic group, by means of —O—, —CO—, —COO—, —CONH—,—CON<, —N═CH— or the like; and the like. At least one of the organicgroups may be a group derived from a polymer as will be described later.The group derived from a polymer may consist of a polymer residueobtained by removing one or more atoms or groups from the polymer, and alinking group for connecting the polymer residue with the quaternaryammonium salt.

No particular limitation is placed on the number of carbon atoms presentin the aliphatic hydrocarbon radicals constituting the aforesaid organicgroups. However, aliphatic hydrocarbon radicals of 1 to 72 carbon atomsare generally preferred partly because the raw materials are readilyavailable. Specific examples include branched and straight-chain alkylgroups such as methyl, ethyl, n- or isopropyl, n-, iso-, sec- ortert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, decyl, dodecyl,tetradecyl, hexadecyl and octadecyl.

Moreover, no particular limitation is placed on the number of carbonatoms present in the aromatic hydrocarbon radicals. However, aromatichydrocarbon radicals of 6 to 20 carbon atoms are generally preferredpartly because the raw materials are readily available. Specificexamples include aryl groups such as phenyl, naphthyl, xylyl, tolyl andstyryl; and aralkyl groups such as benzyl and phenetyl.

Furthermore, no particular limitation is placed on the number of carbonatoms present in the alicyclic hydrocarbon radicals. However, alicyclichydrocarbon radicals of 5 to 18 carbon atoms are preferred. Specificexamples include cyclohexyl and adamantyl groups.

On the other hand, no particular limitation is placed on the number ofcarbon atoms and heteroatoms (e.g., oxygen, sulfur or nitrogen atoms)constituting the rings of the heterocyclic groups. However, saturated orunsaturated heterocyclic groups composed of 2 to 18 carbon atoms and 1to 3 heteroatoms are generally preferred partly because the rawmaterials are readily available. Where a plurality of heteroatoms arepresent, they may be the same or different. Moreover, the heterocyclicgroups may be condenced with a hydrocarbon rings. Specific examples ofsuch heterocyclic groups include, for example, groups derived fromheterocyclic compounds having one heteroatom, such as furan, thiophene,pyrrole and pyridine; groups derived from heterocyclic compounds havingtwo hetero-atoms, such as thiazole, imidazole and pyrimidine; groupsderived from heterocyclic compounds formed by the condensation of aheterocycle and a hydrocarbon ring, such as indole and quinoline; andgroups derived from heterocyclic compounds condensation by thecondensation of heterocycles, such as purine and pteridine.

The quaternary ammonium salt used in the present invention shouldpreferably have low solubility in water, because the resultingbicarbonate ion-sensitive membrane can provide a longer electrode life.For this reason, it is preferable that at least one of R¹ to R⁴ in theforegoing formula (1) be a group derived from a polymer or an organicgroup of 5 to 72 carbon atoms. It more preferable that at least two ofR¹ to R⁴ be organic groups of 5 to 72 carbon atoms.

Although the above-described organic groups may have varioussubstituents, it is desirable that the number of highly polarsubstituents (e.g., hydroxyl and amino) is as small as possible in orderto minimize solubility in water. Moreover, from the viewpoint of thelife of the bicarbonate ion-sensitive membrane, it is desirable that theorganic groups have essentially no highly active substituents (e.g.,halogen, mercapto and amino) or, even if the organic groups have suchsubstituents, their content is as low as possible.

Where the organic groups in the above formula (1) are not groups derivedfrom a polymer, organic groups represented by the following formulae(2a) to (2c) are preferred from the viewpoint of the easy availabilityof raw materials and yield in the synthesis of quaternary ammoniumsalts.

 

wherein A′ is a monovalent aliphatic hydrocarbon radical that may havean ether linkage, or a monovalent aromatic hydrocarbon radical that mayhave an ether linkage; A″ is a divalent aliphatic hydrocarbon radicalthat may have an ether linkage, or a divalent aromatic hydrocarbonradical that may have an ether linkage, Y′ is a hydrogen atom or—R′—X′—A′, B′ is —N<, —CH< or

 

R′ is a divalent or trivalent aliphatic hydrocarbon radical or aromatichydrocarbon radical, X′ is —O—, —CO—, —COO— or —CONH—; i, j, k, l, m andn are each 0 or 1; when a plurality of R′ radicals are present in oneorganic group, the plurality of R′ radicals may be the same ordifferent; and the same shall apply to X′ and A′.

Examples of the aliphatic hydrocarbon radicals and aromatic hydrocarbonradicals represented by A′, A″ and R′ in the above formulae (2a) to (2c)are the same as the various groups described previously in connectionwith the foregoing formula (1).

Among the organic groups represented by the above formulae (2a) to (2c),especially preferred groups are given below.

 

wherein A₁, A₂ and A₃ are each independently an aliphatic hydrocarbonradical of 8 to 30 carbon atoms which may have an ether linkage, e is aninteger of 1 to 18, and c, d, f, g and h are each an integer of 0 to 36.

The quaternary ammonium salts in which at least one of the organicgroups in the above formula (1) is a group derived from a polymer may beeasily prepared, for example, according to any of the followingprocesses.

(A) A process in which a quaternary ammonium salt having a reactivegroup is reacted with a polymer having a group capable of reacting withthe reactive group.

(B) A process in which a tertiary amine serving as a precursor of aquaternary ammonium salt is reacted with a polymer having a group thatforms a quaternary ammonium salt by addition to the tertiary amine.

(C) A process in which a polymer having a primary, secondary or tertiaryamine serving as a precursor of a quaternary ammonium salt is reactedwith a substance having a group that forms a quaternary ammonium salt byaddition to the primary, secondary or tertiary amine.

(D) A process in which a quaternary ammonium salt having a polymerizablegroup is polymerized by a suitable means of polymerization.

(E) A process in which a primary or secondary amine serving as aprecursor of a quaternary ammonium salt is reacted with a polyvalenthalogenated hydrocarbon.

In the aforesaid process (A), examples of the reactive group possessedby the quaternary ammonium salt include hydroxyl, carboxyl, primary orsecondary amino, and haloalkyl groups. Examples of the group on thepolymer, which is capable of reacting complimentarily with thesereactive groups, include haloalkyl, carboxyl, hydroxyl, and primary orsecondary amino groups. As a result of the reaction between thesegroups, the quaternary ammonium salt is introduced into the polymer bymeans of a linking group such as —O—, —CO—, —COO— or —CONH—.

Examples of the polymer having a group capable of reacting with thereactive group possessed by the quaternary ammonium salt includepolymethacrylic acid, polymethyl acrylate-polyhydroxyethyl methacrylatecopolymer, polyhydroxyethyl acrylate-poly-hydroxyethyl methacrylatecopolymer, polyacrylic acid, polyacryl-amide-polyacrylic acid copolymer,polyvinyl alcohol, polyvinyl alcohol-polyethylene copolymer, polyvinylalcohol-polyvinyl acetate copolymer, polyepichlorohydrin,polyallylamine, polyethylene-imine, polyethylene-polymaleic anhydridecopolymer, polymethyl vinyl ether-polymaleic anhydride copolymer,polystyrene-polyallyl alcohol copolymer, polystyrene-polymaleic acidcopolymer, polystyrene-polymaleic anhydride copolymer, polyvinylchloride-polyvinyl acetate copolymer, polyvinyl chloride-polyvinylalcohol copolymer, polyvinylidene chloride-polymethyl acrylatecopolymer, poly-4-vinylphenol, poly-4-vinylpyridine,poly-4-vinylpyridine-polystyrene copolymer,poly-4-vinylpyridine-polybutyl methacrylate copolymer, polyvinylpyrrolidone-polyvinyl acetate copolymer, polychloromethylstyrene, andpolychloromethylstyrene-polyhydroxyethyl methacrylate copolymer.

One specific example of the reaction between such a polymer and aquaternary ammonium salt having a reacting group is the reaction betweenthe hydroxyl group of a hydroxyethyltrioctyl-ammonium salt and thecarboxyl groups of polymethacrylic acid. Thus, there can be synthesizeda polymer into which quaternary ammonium salt groups of the followingformula (4) have been introduced by means of an ester linkage (—COO—).

 

In the aforesaid process (B), the tertiary amine serving as a precursorof a quaternary ammonium salt is a compound of the following formula(5):

 

wherein R¹ to R³ are organic groups as defined above. The group thatforms a quaternary ammonium salt by addition to the tertiary amine maypreferably comprise, for example, a haloaralkyl group (e.g.,chlorobenzyl) or a haloalkyl group (e.g., chloromethyl).

One specific example of the aforesaid process (B) is the reactionbetween a chloromethylstyrene-hydroxyethyl acrylate copolymer andtrioctylamine. Thus, there can be obtained a styrene-hydroxyethylacrylate copolymer into which quaternary ammonium salt groups of thefollowing formula (6) have been introduced.

 

In the aforesaid process (C), examples of the polymer having a primary,secondary or tertiary amine include polyallylamine andpolyethylene-imine. As the substance having a group that forms aquaternary ammonium salt by addition to the primary, secondary ortertiary amine, there may preferably be used a halobenzyl group, ahaloalkyl group or the like. One specific example of the aforesaidprocess (C) is the reaction between polyallylamine and1-bromoocta-decane. Thus, there can be obtained a quaternary ammoniumsalt-containing polymer in which at least some of the amino groupspresent in polyallylamine have been altered to groups of the followingformula (8):

 

In the aforesaid process (D), the polymerizable group may be a vinylgroup or the like. Such polymerizable groups may be polymerized by ameans of polymerization such as radical polymerization. As a specificexample, N,N-dioctadecyl-N-methyl-N-(styryl-methyl)ammonium chloride maybe homopolymerized by radical polymerization in the presence of aradical polymerization initiator such as azobisisobutyronitrile orbenzoyl peroxide. Moreover, quaternary ammonium salts having such apolymerizable group may also be polymerized, for example, by radicalcopolymerization reaction with hydroxyethyl acrylate orN-methylolacrylamide.

In the aforesaid process (E), the primary or secondary amine serving asa precursor of a quaternary ammonium salt is a compound of the followingformula (9) or (10):

 

wherein R¹ and R² are each independently an organic groups as describedpreviously. One specific example of the reaction between such a primaryor secondary amine and a polyvalent halogenated hydrocarbon is thereaction between dioctylamine and 1,4-dibromo-butane.

No particular limitation is placed on the molecular weight of thequaternary ammonium salts prepared in the above-described manner andhaving the form of a polymer. However, from the viewpoint of formabilityinto a membrane material, and the like, it is generally preferable thatthe quaternary ammonium salts have a number-average molecular weight inthe range of 5,000 to 10,000,000, more preferably 10,000 to 10,000,000,and most preferably 20,000 to 10,000,000.

The quaternary ammonium salts in which one of the organic groups in theforegoing formula (1) is a group derived from a polymer includequaternary ammonium salts represented by the following general formulae(11a), (11b) and (11c):

 

wherein R¹ to R³ and A⁻ have the same meanings as defined above, R³′ andR⁴′ are each independently a divalent organic group, X″ is a linkinggroup such as —O—, —CO—, —COO— or —CONH—,

 

is a residue obtained by removing m groups or atoms from the polymer,

 

are each independently a residue obtained by removing one group or atomfrom the polymer, m is an integer of 1 or greater, n is 0 or 1, and Q isan integer of 1 or greater.

When the above formulae (11a) and (11b) are compared with the foregoingformula (1), it can be seen that

 

in the above formula (11a) corresponds to —R⁴ in formula (1), and

 

in the above formula (11b) correspond to —R³ and —R⁴, respectively, informula (1).

As the polymer residues

 

in the above formulae (11a) and (11b), resides derived from homopolymersor copolymers containing repeating units represented by the followingformula (12a), (12b) or (12c) are preferred.

 

wherein X′″ is a hydrogen atom, a fluorine atom, a chlorine atom, analkyl group of 1 to 6 carbon atoms, or a cyano group, and this group canbe joined to a quaternary ammonium salt by a bond marked with anasterisk (*). The plurality of X′″ radicals may be the same or differentfrom each other.

Besides the above-described quaternary ammonium salts, pyridinium salts,phosphonium salts and sulfonium salts can also be used as onium saltcompounds in the present invention. The pyridinium salts, phosphoniumsalts and sulfonium salts which can preferably be used in the presentinvention include compounds of the following formulae (13) to (15).

 

wherein R⁵ to R¹⁷ are each independently a hydrogen atom or an organicgroup, and A⁻ is an anion.

The aforesaid organic groups can be the same as the organic groupsdescribed in connection with the foregoing formula (1). In each of theabove formulae (13) to (15), at least one of the organic groups may be agroup derived from a polymer as described previously. Similarly to thepreviously described quaternary ammonium salts, it is also preferable inthe aforesaid pyridinium salts, phosphonium salts and sulfonium saltsthat one of the organic groups in formulae (13) to (15) is a groupderived from a polymer, or these onium salt compounds have one or more,more preferably two or more, organic groups of 5 to 72 carbon atoms,because they have low solubility in water and can hence enhance thedurability of the resulting electrode. Moreover, the aforesaid organicgroups may have various substituents. However, in order to minimizesolubility in water, it is desirable that the organic groups haveneither highly active substituents (e.g., halogen, mercapto and amino)nor highly polar substituents (e.g., hydroxyl and amino), or even if theorganic groups have such substituents, their content is as low aspossible.

Preferred examples of the organic groups in the above formulae (13) to(15) are the groups represented by the foregoing formulae (2a) to (2c)and, in particular, the groups represented by formulae (3a) to (3r).

Aromatic Boric Diester Structural Unit (B)

In the polymer membrane in accordance with the present invention, thearomatic boric diester structural unit (B) may be present in the form ofa low-molecular-weight compound or in a form introduced into the polymermolecule. In the present description, the aromatic boric diesterstructural units in both forms are collectively referred to as “aromaticboric diester compounds”.

By allowing an aromatic boric diester compound to coexist with theabove-described onium salt compound in the polymer membrane, the polymermembrane can exhibit excellent selectivity to bicarbonate ion(hydrogencarbonate ion) when it is used as an anion-sensitive membrane.

The aromatic boric diester compounds which can be used in the presentinvention include compounds of the following formula (16).

 

wherein X¹ and X² are each independently an organic group, or X¹ and X²are combined with the atoms adjacent thereto so as to form a ringstructure, Ar′ is an aromatic hydrocarbon radical, Z is a hydrogen atomor an organic group, and s is an integer of 1 or greater.

The explanation previously given for the organic groups represented byR¹ to R⁴ in the foregoing formula (1) is directly applicable to theorganic groups represented by X¹, X² and/or Z in the above formula (16).Similarly to R¹ to R⁴, the organic groups represented by X¹, X² and/or Zmay also be groups derived from a polymer.

Moreover, where X¹ and X² contain a polymerizable double bond, thearomatic boric diester compound may be in the form of a polymerconsisting of repeating units derived from the above formula (16). Inthis case, the repeating units connected to the unit of interest derivedfrom formula (16) are regarded herein as “organic groups” forconvenience sake.

The organic groups represented by X¹, X² and/or Z in the above formula(16) may have one or more substituents. Such substituents include, forexample, halogen, nitro, cyano, hydroxyl, mercapto, amino and imino.Although there is no limit to the number of substituents, it ispreferable from the viewpoint of ease of synthesis, low solubility inwater, and the like that the number of highly active substituents (e.g.,halogen, mercapto and amino) and highly polar substituents (e.g.,hydroxyl and amino) be as small as possible.

Where X¹ and X² in the above formula (16) are combined with the atomsadjacent thereto so as to form a ring structure, the ester moiety of thearomatic boric diester compound is less susceptible to hydrolysis.Moreover, the bicarbonate ion-sensitive membrane of the presentinvention provides a more stabilized electric potential response and,furthermore, has good compatibility with polymers having amembrane-forming ability as will be described later. Consequently, thismembrane is preferable in that it has the advantage of providing a longelectrode life.

Thus, the aromatic boric diester compounds which can preferably be usedin the present invention include compounds of the following formula(17):

 

in which X is a divalent organic group of two or more carbon atoms, andAr′, Z and s have the same meanings as defined for the above formula(16).

Where X in the above formula (17) has a polymerizable unsaturated group(e.g., a vinyl group) as a pendant side chain, the compound of the aboveformula (17) may also be present in the form of a polymer which isformed by the polymerization of two or more molecules of the compoundand hence consists of repeating units of the following formula (18):

 

wherein Y is a group derived from a compound having a groupcopolymerizable with the polymerizable unsaturated group possessed by X,X has the same meaning as defined for the above formula (17), and Ar′, Zand s have the same meanings as defined for the foregoing formula (16).

In the above formulae (17) and (18), it is preferable from the viewpointof stability that the ring formed by X and a boric diester moiety(—O—B—O—) be a five-membered or six-membered ring, i.e., the numer ofatoms constituting that part of the ring which is formed by X be 2 or 3.Among others, it is most preferable from the viewpoint of easyavailability of raw materials, yield in synthesis, and the like that Xbe an ethylene or trimethylene group which may have one or moresubstituents.

Specific examples of X include groups represented by the followingformulae (19a) and (19b):

 

wherein M₁, M₂, M₃, M₄, M₅ and M₆ are each independently a hydrogen atomor an organic group.

Examples of the organic groups represented by M₁, to M₆ in the aboveformulae (19a) and (19b) include aliphatic hydrocarbon radicals such asmethyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, octyl, decyl,dodecyl, tetradecyl, hexadecyl and octadecyl; aromatic hydrocarbonradicals such as phenyl, naphthyl, xylyl and benzyl; alicyclichydrocarbon radicals such as cyclohexyl and adamantyl; heterocyclicgroups derived from furan, thiophene, pyrrole, pyridine and like rings;and groups formed by joining these groups to each other by means of —O—,—CO—, —COO—, —CONH—, —CON< or —N═CH—. Moreover, at least one of theorganic groups represented by M₁ to M₆ may be a group derived from apolymer. Among these organic groups, a hydrogen atom and strach-chain orbranched aliphatic hydrocarbon radicals of 1 to 36 carbon atoms areespecially preferred from the viewpoint of ease of synthesis.

The divalent organic groups of two or more carbon atoms which arerepresented by X in the above formula (17)and are especially preferredfor use in the present invention include groups represented by thefollowing formulae (20a) to (20s):

 

wherein X³ is an aliphatic hydrocarbon radical or a group derived from apolymer; when a plurality of X³ radicals are present in the samestructure, they may be different from each other; and p is an integer of1 to 4.

As the group derived from a polymer which is represented by X³, theremay be used any of the groups derived from a polymer which werepreviously described in connection with the organic groups in thequaternary ammonium salts of the foregoing formula (1).

Examples of the aromatic hydrocarbon radical represented by Ar′ in theforegoing formulae (16) to (18) include groups derived from aromatichydrocarbon rings of 6 to 10 carbon atoms, such as benzene, toluene,xylene and naphthalene rings. Among others, the aromatic boric diestercompounds in which Ar′ is an aromatic hydrocarbon radical derived from abenzene or naphthalene ring are especially preferred because they show agood yield in the synthesis thereof Moreover, these aromatic boricdiester compounds themselves have improved stability and consequentlyprovide a stabilized electric potential response.

Although the aromatic hydrocarbon radical may have one or moresubstituents other than Z, it is preferable from the viewpoint of yieldin synthesis and the like that the number of substituents is as small aspossible. Preferred substituents include, for example, a halogen atom(e.g., chlorine), a nitrile group and a nitro group. Moreover, thepreferred number of substituents is 2 or less.

In the above formulae (16) to (18), Z is a hydrogen atom or an organicgroup. Examples of the organic group include aliphatic hydrocarbonradicals such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,octyl, decyl, dodecyl, tetradecyl, hexadecyl and octadecyl; aromatichydrocarbon radicals such as phenyl, naphthyl, xylyl and benzyl;alicyclic hydrocarbon radicals such as cyclohexyl and adamantyl;heterocyclic groups derived from furan, thiophene, pyrrole, pyridine andlike rings; and groups formed by combining these groups with —O—, —CO—,—COO—, —CONH—, —CON< or —N═CH—. Moreover, the organic group may be agroup derived from a polymer.

The aromatic boric diester compounds in which, among these organicgroups, Z is a group containing an unsubstituted or substituted brahchedor straight-chain hydrocarbon radical of 1 to 72 carbon atoms arepreferred because they show an improvement in compatibility withpolymers having a membrane-forming ability as will be described later.Moreover, the aromatic boric diester compounds in which Z is a brahchedor straight-chain alkyl group of 1 to 72 carbon atoms having —O—, —CO—,—COO—, —CONH—, —CON< or —N═CH— are preferred because raw materials forthe synthesis thereof are readily available and they show a good yieldin the systhesis thereof.

Where the aromatic hydrocarbon radical represented by Ar′ is a phenylenegroup, Z in the above formulae (16) and (17) can be attached to the o-,n- or p-pisition with respect to the boron atom. Where the aromatichydrocarbon radical represented by Ar′ is a naphthyl group, Z can beattached to any of the carbon atoms located at the 1- to 8-positions.

No particular limitation is placed on the number (s) of Z radicalsattached to Ar′. However, from the viewpoint of yield in synthesis, andthe like, s is preferably in the range of 1 to 3.

The groups which are represented by Z and can preferably be used in thepresent invention include, for example, groups represented by thefollowing formulae (21a) to (21j):

 

wherein Z₁ is an aliphatic hydrocarbon radical of 1 to 72 carbon atoms,a group formed by joining two aliphatic hydrocarbon radicals to eachother by means of —O—, —CO— or —COO—, or —CH₂(OCH₂CH₂)_(n)—OCH₃ (inwhich n is an integer of 1 to 10).

As Z₁ in the above formulae (21a) to (21j), there may be used a groupsuitably chosen from the groups of formulae (3a) to (3r) which werepreviously described in connection with the quaternary ammoniumcompounds of formula (1).

In an especially preferred embodiment of the present invention, Z₁ inthe above formulae (21a) to (21j) is a bracnhed alkyl group of 8 to 18carbon atoms. In this case, the resulting aromatic boric diestercompound has excellent compatibility with polymers as will be describedlater, and hence provides a more stabilized electric potential response.Examples of the bracnhed alkyl group of 8 to 18 carbon atoms include2-ethylhexyl, 3,7-dimethyloctyl, 2-butyloctyl and 2-hexyldecyl groups.

In the foregoing formula (17), the groups represented by X, Ar′ and Zmay be any combination of groups. However, with consideration for thestability of the bicarbonate ion-sensitive membrane of the presentinvention, selectivity to hydrogencarbonate ion, yield in synthesis,easy availability of raw materials, and the like, aromatic boric diestercompounds of the following formulae (22a) and (22b) are especiallypreferred.

 

wherein M₁′, M₂′, M₃′, M₄′, M₅′ and M₆′ are each independently ahydrogen atom, a methyl group, or a group derived from a polymer, Ar′ isan aromatic hydrocarbon radical, and Z is any of the groups of the aboveformulae (21a) to (21j).

The aromatic boric diester compounds which can be used in the presentinvention may be synthesized according to any of per se known processes.However, the following exemplary process of synthesis can preferably beemployed.

First of all, an aromatic boric acid compound is synthesized by reactinga bromoaryl compound with a trialkoxyborane in the presence ofn-butyllithium. Then, this aromatic boric acid compound is convertedinto a cyclic diester of the aromatic boric acid by reacting it with alow-molecular-weight diol compound such as ethylene glycol orpropanediol, or a high-molecular-weight diol compound such as polyvinylalcohol or a compound obtained by functionalizing some hydroxyl groupsof a high-molecular-weight diol compound such as polyvinyl alcohol(e.g., by esterification). Furthermore, the desired aromatic boricdiester compound can be purified from the reaction mixture by columnchromatography using silica gel particles as the stationary phase, or bydistillation, recrystallization or the like. As the developing solventfor this purpose, well-known solvents such as chloroform, acetone andmethanol may be used alone or in admixture of two or more.

Where an aromatic boric diester having a high molecular weight isdesired, the aromatic boric diester compound can be obtained in the formof a homopolymer or copolymer, for example, by preparing a cyclic esterof an aromatic boric acid having a polymerizable group (e.g.,4-vinylphenylboric acid) according to the above-described process andthen polymerizing this ester compound alone, or by copolymerizing theaforesaid ester compound with another compound having polymerizability.These polymeric compounds may be easily synthesized by employing anypolymerization technique that is suitably chosen from the commonpolymerization techniques for the synthesis of polymers (e.g., radicalpolymerization, cationic polymerization, and anionic polymerization),according to the compound used. Generally, radical polymerization in thepresence of a radical initiator (e.g., azobisisobutyronitrile) isespecially preferred because of the ease of control of the polymerstructure, the convenience of polymerization, and the like. The desiredaromatic boric diester compound can be obtained by purifying theresulting polymeric compound by column chromatography using silica gelparticles as the stationary phase, or by a suitable means such asdistillation or recrystallization. As the developing solvent for thispurpose, well-known solvents such as chloroform, acetone and methanolmay be used alone or in admixture of two or more.

The purity of an aromatic boric diester compound can be confirmed byanalysis using thin-layer chromatography (hereinafter abbreviated asTLC). Silica gel or alumina is suitably used as the support for TLCanalysis. As the developing solvent, well-known solvents such aschloroform, acetone and methanol may be used alone or in admixture oftwo or more. Moreover, the structure of an aromatic boric diester can bedetermined by using proton NMR spectroscopy suitably in combination withelemental analysis or gel permeation chromatography.

In a specific embodiment of the above-described aromatic boric diestercompound, there is a compound in which an onium salt structural unit(A), particularly a quaternary ammonium salt structural unit, coexistswith an aromatic boric diester structural unit (B) in one molecule. Thiscompound, when used alone, can produce a similar effect to that of amixture of an onium salt compound and an aromatic boric diestercompound. Specific examples of this compound include aromatic boricdiester compounds of the following formulae (23) to (25):

 

wherein at least one of L₁ to L₅ is a branched or straight-chain alkylgroup of 1 to 72 carbon atoms which may have —O—, —CO—, —COO—, —CONH—,—CON< or —N═CH—, and the others are hydrogen atoms; L₆ is a groupcontaining a quaternary ammonium salt group; L₇ is a divalent organicgroup of 1 to 8 carbon atoms; L₈ is a hydrogen atom or an alkyl group of1 to 3 carbon atoms; m is 0 or 1; and 0<x≦1. It is to be understood thatthe repeating units whose proportions are designated by x and 1−x may bepresent alternately, randomly or in blocks.

Examples of the branched or straight-chain alkyl group of 1 to 72 carbonatoms represented by L₁ to L₅ in the above formulae include methyl,ethyl, propyl, 2-ethylhexyl, dodecyl, tetradecyl and octadecyl. Examplesof the branched or straight-chain alkyl group of 1 to 72 carbon atomshaving —O—, —CO—, —COO—, —CONH—, —CON< or —N═CH— include methoxy,ethoxy, propoxy, 2-ethylhexyloxy, dodecyloxy, tetradecyloxy andoctadecyloxy.

Examples of the group represented by L₆ include groups derived fromquaternary ammonium salts of the foregoing formula (1). Examples of thedivalent organic group represented by L₇ include aliphatic hydrocarbonradicals such as methylene, ethylene, trimethylene, tetramethylene,pentamethylene, hexamethylene, heptamethylene, octamethylene andpropylene; aromatic hydrocarbon radicals such as phenylene andnaphthylene; and groups obtained by joining similar or different ones ofthese groups by means of —O—, —CO—, —COO—, —CONH—, —CON< or —N═CH—.

Examples of the alkyl group of 1 to 3 carbon atoms represented by L₈include methyl, ethyl and propyl.

x may be greater than 0 and not greater than 1. However, in order toenhance selectivity to bicarbonate ion, it is especially preferably thatx be in the range of 0.2 to 1.0.

No particular limitation is placed on the molecular weights of thearomatic boric diester compounds of the above formulae (23) to (25).However, in order to obtain aromatic boric diester compounds having asufficient membrane-forming ability by themselves, it is generallypreferable that they have a number-average molecular weight in the rangeof 5,000 to 1,000,000,000 and more preferably 5,000 to 10,000,000.

Among the boric diester compounds represented by the above formulae (23)to (25), the aromatic boric diester compounds in which one of L₁ to L₅is a 2-ethylhexyloxy, dodecyloxy, tetradecyloxy or octadecyloxy groupand the others are hydrogen atoms, L₆ is aN,N,N,N-(oxycarbonylethyl)dioctadecylmethylammonium,N,N,N,N-(oxycarbonylmethyl)dioctadecylmethylammonium,N,N,N,N-(carbonyloxyethyl)dioctadecylmethylammonium or N, N, N,N-(p-benzyl)-dioctadecylmethylammonium group, L₇ is an oxymethylene,methyleneoxymethylene, carbonyloxymethylene or phenylene group, L₈ is ahydrogen atom or a methyl group, and x is in the range of 0.9 to 0.5 areespecially preferred from the viewpoint of formability into a membrane,ease of synthesis, and the like.

Bicarbonate Ion-sensitive Membrane

The bicarbonate ion-sensitive membrane of the present invention maycomprise a polymer membrane containing the above-described onium saltstructural unit (A) and aromatic boric diester structural unit (B) inthe formed of low-molecular-weight compounds dispersed in the polymer orin a form introduced into a polymer molecule.

In one embodiment, the sensitive membrane of the present invention maycontain an onium salt compound and an aromatic boric diester compound ina form dispersed in a suitable polymer matrix.

However, where one or both of the onium salt compound and the aromaticboric diester compound are membrane-forming polymers, at least a part,or essentially all in some cases, of the polymer matrix may be omitted.Whether the use of the polymer matrix should be omitted or not may besuitably determined on the basis of the properties required of thesensitive membrane, and the like.

Thus, examples of the bicarbonate ion-sensitive membrane of the presentinvention include:

{circle around (1)} a membrane comprising a polymer matrix in which alow-molecular-weight onium salt compound and a low-molecular-weightaromatic boric diester compound are dispersed;

{circle around (2)} a membrane comprising a low-molecular-weight oniumsalt compound and a high-molecular-weight (polymeric) aromatic boricdiester compound, and optionally containing another polymer matrix;

{circle around (3)} a membrane comprising a high-molecular-weight(polymeric) onium salt compound and a low-molecular-weight aromaticboric diester compound, and optionally containing another polymermatrix;

{circle around (4)} a membrane comprising a high-molecular-weight(polymeric) onium salt compound and a high-molecular-weight (polymeric)aromatic boric diester compound; and

{circle around (5)} a membrane comprising a polymer in which the oniumsalt structural unit (A) and the aromatic boric diester structural unit(B) coexist in the same molecule.

The proportions in which the onium salt structural unit (A) and thearomatic boric diester structural unit (B) are present in thebicarbonate ion-sensitive membrane of the present invention may besuitably chosen on the basis of the performance desired for thesensitive membrane, and the like. However, these proportions shouldgenerally desirably be such that, whether the aforesaid structural units(A) and (B) are present in the form of low-molecular-weight compounds orin a form introduced into a polymer molecule, the ratio of [the numberof moles of the aromatic boric diester structural unit (B)] to [thenumber of moles of the onium salt structural unit (A)] is at least 0.01,preferably in the range of 0.1 to 100,000, and more preferably in therange of 0.3 to 10,000.

It is desirable that the polymer which may be used as the matrix in thesensitive membrane of the present invention is a membrane-formingpolymer having essentially no solubility in water, because the membraneis usually used in aqueous solutions. The polymers which can be used inthe present invention include, for example, homopolymers or copolymersof vinyl halides such as vinyl chloride, vinyl bromide and vinylidenechloride; homopolymers or copolymers of unsubstituted and substitutedstyrenes such as styrene, chlorostyrene and bromostyrene; homopolymersor copolymers of acrylic and methacrylic esters such as methyl acrylate,ethyl acrylate, ethyl methacrylate and butyl methacrylate; homopolymersor copolymers of vinyl esters such as vinyl acetate; polymers of dienessuch as butadiene and isoprene, and copolymers of such a diene andstyrene, acrylonitrile or the like; polyurethanes; siloxane polymers orcopolymers; and cellulose derivatives such as cellulose acetate andcellulose nitrate. These polymers may be used alone or in admixture oftwo or more.

Among the above-described membrane-forming polymers, homopolymers orcopolymers of vinyl halides and siloxane polymers or copolymers areespecially preferred because they can provide a longer life to thebicarbonate ion-sensitive membrane of the present invention when it isused in biological fluids.

Where a polymer matrix as described above is used in the sensitivemembrane of the present invention, the contents of the onium saltcompound and the boric diester compound in the sensitive membrane mayvary according to the end use of the sensitive membrane, and the like.However, it is generally preferable to use the polymer matrix in anamount of 1 to 70 parts by weight, more preferably 1 to 60 parts byweight, and most preferably 1 to 50 parts by weight, per 100 parts byweight of the combined amount of the onium salt compound, the aromaticboric diester compound and the polymer matrix.

Moreover, a fat-soluble anion salt may preferably be incorporated intothe bicarbonate ion-sensitive membrane of the present invention asrequired. This makes it possible to further improve the response speedto ions of the sensitive membrane of the present invention and measurethe ion concentrations in samples more rapidly. To this end, thefat-soluble anion preferably comprises one which has a negativelycharged atomic group in the molecule and which is soluble in organicsolvents such as chloroform and hexane. This fat-soluble anion is usedas a salt formed from the fat-soluble anion and a counter cation.

The fat-soluble anion salt should preferably have low solubility inwater, because the resulting anion-sensitive membrane has a longer life.It is preferable that the solubility in water of the fat-soluble anionsalt used in the present invention be not greater than 10, morepreferably not greater than 1, and most preferably not greater than0.01. The term “solubility” as used herein refers to the maximum weight(g/dl) of the solute present in a saturated solution of a fat-solubleanion sodium salt at 20° C.

The fat-soluble anion salts which can be used in the present inventioninclude, for example, tetraphenyl borates such astetrakis[3,5-bis(trifluoromethyl)phenyl]borate,tetrakis(4-chlorophenyl)borate, tetrakis(4-fluorophenyl)borate andtetraphenyl borate; salts of long-chain alkylsulfonic acids such asdecylsulfonic acid, dodecylsulfonic acid, dodecylbenzenesulfonic acid,octadecylsulfonic acid and oleylsulfonic acid; salts of long-chaindialkylsulfosuccinic acids such as bismethylhexylsulfosuccinic acid,dioctylsulfosuccinic acid, didecylsulfosuccinic acid anddidodecylsulfosuccinic acid; salts of long-chain alkylphosphonic acidssuch as decylphosphonic acid, dodecylphosphonic acid,dodecylbenzenephosphonic acid, octadecylphosphonic acid andoleylphosphonic acid; salts of long-chain dialkylphosphonic acids suchas bismethylhexylphosphonic acid, dioctyiphosphonic acid,didecylphosphonic acid and didodecylphosphonic acid; and salts oflong-chain dialkylphosphosuccinic acids such asbismethylhexylphosphosuccinic acid, dioctylphosphosuccinic acid,didecylphosphosuccinic acid and didodecylphosphosuccinic acid. Among theabove-described fat-soluble anion salts, tetraphenyl borates arepreferably used because they have low solubility in water and can henceprovide electrode having high durability.

As the counter cation for the aforesaid fat-soluble anion, anywell-known cation may be used without limitation. However, potassium andsodium ions are preferred because they have good solubility in anorganic solvent used for membrane formation.

No particular limitation is placed on the content of the fat-solubleanion salt in the sensitive membrane of the present invention. However,if the molar ratio of the fat-soluble anion salt based on the onium saltcompound [i.e., (the number of moles of the fat-soluble anion salt)/(thenumber of moles of the onium salt compound)] is less than 0.01, theaddition of the fat-soluble anion salt will produce no effect. If it isgreater than 1, the resulting membrane will show a reduction inresponsivity to ions and may sometimes lose its responsivity to ions.Accordingly, it is generally preferable that the aforesaid molar ratiobe in the range of 0.1 to 0.7 and more preferably 0.2 to 0.7.

The sensitive membrane of the present invention may be formed insubstantially the same manner as the membrane formation of per se knownpolymers. According to one exemplary and preferred method, the oniumsalt compound and the aromatic boric diester compound, as well as thepolymer and fat-soluble anion salt which may be added as required, aredissolved in an organic solvent. After this solution is spread or castover a planar surface, the organic solvent is evaporated to form amembranous material.

As the aforesaid organic solvent, any organic solvent may be usedwithout limitation, provided that it can dissolve the onium saltcompound and the aromatic boric diester compound, as well as the polymerand fat-soluble anion salt which may be added as required. Specificexamples of the organic solvents which can generally and preferably beused include tetrahydrofuran, dioxane, chloroform, methylene chloride,dimethylformamide, dimethylacetamide, benzene and toluene.

The membranous material obtained according to the above-described methodgenerally comprises a transparent or white homogeneous membrane, andthis membranous material can be directly used as an anion-sensitivemembrane. The membrane thickness can be controlled by regulating theamounts of ingredients used and the membrane area. However, withconsideration for the operability of the resulting ion-selectiveelectrode, and the like, the membrane thickness is preferably in therange of 1 μm to 1 mm and more preferably 2 to 606 μm.

The bicarbonate ion-sensitive membrane of the present invention, whichis formed in the above-described manner, can be applied to ion-selectiveelectrodes having a well-known construction. Generally, the membrane ispreferably used in an ion-selective electrode constructed by providing avessel comprising a cylindrical electrode body fitted with the sensitivemembrane in at least that part thereof which is to be immersed in asample solution, and filling the vessel with an internal referenceelectrode and an internal electrolyte or ionic conductive substance. Inthis electrode, no particular limitation is placed on the materials ofthe components other than the anion-sensitive membrane, and there may beused any of per se known materials. As the internal reference electrode,there may be used, for example, an electrically conductive substancesuch as platinum, gold or carbon graphite, or a hardly soluble metalchloride such as silver-silver chloride or mercury-mercury chloride. Asthe internal electrolyte, there may preferably be used, for example, anaqueous solution of a metallic salt such as an aqueous sodium chloridesolution, an aqueous potassium chloride solution or an aqueous sodiumhydrogencarbonate solution. Examples of suitable ionic conductivesubstances include electrical conductors such as gold, platinum andgraphite; and ionic conductors such as silver chloride and mercurychloride. Moreover, as the material of the cylindrical electrode body,there may be used, for example, polyvinyl chloride or polymethylmethacrylate.

A typical example of an ion-selective electrode is illustrated in FIG.1. The ion-selective electrode of FIG. 1 is constructed by providing avessel comprising a cylindrical electrode body 11 fitted with ananion-sensitive membrane 12 at the bottom thereof, filling the vesselwith an internal electrolyte 13, and disposing an internal referenceelectrode 14 therein. Reference numeral 15 designates an O-ring used forliquid-tight sealing purposes.

The ion-selective electrodes to which the bicarbonate ion-sensitivemembrane of the present invention can be applied are not limited to theconstruction illustrated in FIG. 1, but there may be used any type ofion-selective electrode having an anion-sensitive membrane. Othersuitable ion-selective electrodes include, for example, ion-selectiveelectrodes constructed by affixing the bicarbonate ion-sensitivemembrane of the present invention directly to an electrical conductor(e.g., gold, platinum or graphite) or an ionic conductor (e.g., silverchloride or mercury chloride).

An ion-selective electrode utilizing the bicarbonate ion-sensitivemembrane of the present invention may be used according to any of per seknown methods. For example, the ion-selective electrode may be used in amanner illustrated in FIG. 2. Specifically, an ion-selective electrode21, together with a salt bridge 22, is immersed in a sample solution 23.The other end of the salt bridge, together with an external referenceelectrode 24, is immersed in a saturated potassium chloride solution 26.As the aforesaid external reference electrode, there may be used any perse known electrode. Preferred examples thereof include a calomelelectrode, a silver-silver chloride electrode, a platinum plate andcarbon graphite.

As described above, the bicarbonate ion-sensitive membrane of thepresent invention is formed from a composition which comprises an oniumsalt compound and an aromatic boric diester compound, and may furthercontain a membrane-forming polymer and a fat-soluble anion salt asrequired. This membrane has significantly high responsivity tobicarbonate (or hydrogencarbonate) ion relative to interfering ions(e.g., sulfate, nitrate, chloride and salicylate ions) present inbiological fluids such as blood and urine, and further shows a very highresponse speed.

Although the reason why bicarbonate (or hydrogencarbonate) ions can bespecifically detected by using the bicarbonate ion-sensitive membrane ofthe present invention has not been clearly understood, the selectiveresponsivility to bicarbonate ion is a phenomenon which occurs only as aresult of the combined use of an aromatic boric diester compound and anonium salt compound. Accordingly, it is believed that the function of anaromatic boric diester compound as an electron-accepting substancecontributes to the high selectivity to bicarbonate (orhydrogencarbonate) ion.

Consequently, the sensitive membrane of the present invention permitshydrogencarbonate ions contained in biological fluids such as blood andurine to be rapidly determined with very high accuracy.

EXAMPLES

The present invention is more specifically explained with reference tothe following examples. However, these examples are not to be construedto limit the scope of the invention. The meanings of the symbols used inthese examples are as follows.

Proton NMR: ¹NMR

In NMR spectra:

Singlet: s

Doublet: d

Multiplet: m

Benzene ring: phe

Salicylate ion: Sal⁻

Polyvinyl chloride: PVC

Polyvinylidene chloride: PVdC

2-Nitrophenyl octyl ether: NPOE

Tetraoctylammonium bromide: TOABr

Trioctyltin chloride: TOTC

Tetraoctadecylammonium bromide: TOAB

Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate sodium salt: TFPB

Tetrakis[4-chlorophenyl]borate potassium salt: TCPB

Sodium di(2-ethylhexyl)sulfosuccinate: DESS

The various compounds used in the examples are summarized in Tables 1 to23 below. In Tables 1 to 23, the weight-average molecular weight of ahigh-molecular-weight compound as determined by gel permeationchromatography is designated by MW, and the proportions of repeatingunits in the molecule as determined by NMR or elemental analysis aredesignated by x and y. It is to be understood that the repeating unitswhose proportions are designated by x and y may be present alternately,randomly or in blocks.

TABLE 1 Compound No. Structure of onium salt compound 1 CH₃N⁺(n-C₈H₁₇)₃Cl⁻ 2 (n-C₈H₁₇)₄N⁺ Br⁻ 3 (n-C₁₈H₃₇)₄N⁺ Br⁻ 4

5

6

7

8

 

TABLE 2 Compound No. Structure of onium salt compound 9

10

11

 

TABLE 3 Compound No. Structure of onium salt compound 12

13

14

15

 

TABLE 4 Compound No. Structure of onium salt compound 16 (n-C₁₂H₂₅)₄P⁺Cl⁻ 17 (n-C₁₈H₃₇)₃S⁺ Cl⁻ 18 (n-C₁₈H₃₇)₄P⁺ Cl⁻ 19

20

21

22

 

TABLE 5 Compound No. Structure of boric diester compound 23

24

25

26

27

28

29

 

TABLE 6 Compound No. Structure of boric diester compound 30

31

32

33

 

TABLE 7 Compound No. Structure of boric diester compound 34

35

 

TABLE 8 Compound No. Structure of boric diester compound 36

37

38

39

 

TABLE 9 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-2.2(m, alkyl- CH₃, alkyl-CH₂, alkyl-CH, OOC— CH₂),3.3-3.5(m, N⁺—CH₃, N⁺—CH₂), 3.8-4.1(m, phe-O—CH₂, COO—CH), Com- 4.6(m,BO—CH), 6.9, 7.8(bs, phe-H) pound Elemental analysis (C %, H %, N %) No.x y MW Found values Calculated values 40 0.9 0.1 382000 71.25, 9.41,0.69 71.33, 9.52, 0.41 41 0.7 0.3 568000 71.27, 10.16, 1.14 71.04,10.35, 0.99 42 0.5 0.5 728000 70.59, 10.88, 1.24 70.84, 10.91, 1.38

 

TABLE 10 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-2.3(m, alkyl- CH₃, alkyl-CH₂, alkyl-CH, OOC— CH₂,phe-CH₃), 3.3-3.5(m, N⁺—CH₃, N⁺—CH₂), 3.8-4.0(m, phe-O—CH₂, Com-COO—CH), 4.6(m, BO—CH), 6.5(bs, phe-H) pound Elemental analysis (C %, H%, N %) No. x y MW Found values Calculated values 43 0.9 0.1 42300072.55, 9.76, 0.51 72.31, 9.84, 0.38 44 0.7 0.3 592000 71.88, 10.28, 1.1371.68, 10.52, 0.94 45 0.5 0.5 732000 70.99, 10.74, 1.25 71.24, 11.00,1.34

 

TABLE 11 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl- CH₃, alkyl-CH₂), 2.2(t, OOC—CH₂),3.3-4.0(m, N⁺—CH₃, N⁺—CH₂, phe-O— CH₂, O—CH₂CH₂—O, O—CH₃, COO—CH), Com-4.6(m, BO—CH, phe-CH₂), 6.8(s, phe-H) pound Elemental analysis (C %, H%, N %) No. x y MW Found values Calculated values 46 0.9 0.1 74000068.16, 10.19, 0.50 68.23, 10.22, 0.20 47 0.7 0.3 852000 69.00, 10.48,0.89 68.75, 10.56, 0.59 48 0.5 0.5 952000 68.98, 11.12, 1.20 69.26,10.90, 0.99

 

TABLE 12 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl- CH₃, alkyl-CH₂), 2.2(m, OOC—CH₂),3.3-3.5(m, N⁺—CH₃, N⁺—CH₂), 3.8-4.1 (m, phe-O—CH₂, COO—CH), 4.6(m, Com-BO—CH), 6.9, 7.8(bs, phe-H) pound Elemental analysis (C %, H %, N %) No.x y MW Found values Calculated values 49 0.9 0.1 500000 75.02, 10.88,0.54 75.17, 10.79, 0.30 50 0.7 0.3 621000 73.59, 11.23, 1.10 73.77,11.08, 0.80 51 0.5 0.5 764000 72.87, 11.53, 1.01 72.63, 11.32, 1.21

 

TABLE 13 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.2(t, OOC—CH₂),3.3-3.5(m, alkyl-O— CH₂, alkyl-O—CH, N⁺—CH₃, N⁺— CH₂), 3.9(bs,phe-O—CH₂), 4.0 (m, COO—CH), 4.6(m, BO—CH), Com- 6.9, 7.8(bs, phe-H)pound Elemental analysis (C %, H %, N %) No. x y MW Found valuesCalculated values 52 0.9 0.1 485000 74.39, 10.85, 0.57 74.66, 10.72,0.30 53 0.7 0.3 619000 72.32, 10.96, 0.58 72.44, 10.88, 0.79 54 0.5 0.5792000 70.47, 10.94, 1.35 70.68, 11.01, 1.18

 

TABLE 14 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl- CH₃, alkyl-CH₂), 3.6-4.0(m, N⁺—CH₃,N⁺—CH₂, phe-O—CH₂, COO—CH), 4.6 (m, BO—CH), 5.1(bs, OOC—CH₂—N⁺), Com-6.9, 7.8(bs, phe-H) pound Elemental analysis (C %, H %, N %) No. x y MWFound values Calculated values 55 0.9 0.1 548000 74.89, 10.64, 0.5775.14, 10.78, 0.30 56 0.7 0.3 609000 73.77, 11.31, 0.63 73.67, 11.06,0.81 57 0.5 0.5 792000 72.46, 11.14, 1.07 72.47, 11.28, 1.22

 

TABLE 15 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl- CH₃, alkyl-CH₂), 2.2(bs, OOC— CH₂),3.3-4.1(m, alkyl-O—CH₂, alkyl-O—CH, N⁺—CH₃, N⁺—CH₂, phe- O—CH₂), 4.0(m,COO—CH), 4.6(m, BO—CH₂), 6.9, 7.8(bs, phe-H) Compound Elemental analysis(C %, H %, N %) No. x y MW Found values Calculated values 58 0.9 0.1564000 73.69, 10.58, 0.19 73.85, 10.75, 0.27 59 0.7 0.3 695000 73.12,10.85, 0.70 72.92, 11.03, 0.74 60 0.5 0.5 858000 71.98, 11.53, 1.4172.12, 11.27, 1.15

 

TABLE 16 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.2 (m, OOC—CH),3.3-4.0(m, N⁺—CH₃, N⁺—CH₂, phe-O—CH₂, COO—CH), 4.6(m, BO—CH₂), 6.9,7.8(bs, phe-H) Compound Elemental analysis (C %, H %, N %) No. x y MWFound values Calculated values 61 0.9 0.1 188000 72.36, 10.51, 0.5472.43, 10.25, 0.26 62 0.7 0.3 196000 72.14, 10.77, 1.00 71.92, 10.66,0.72 63 0.5 0.5 210000 71.19, 10.83, 1.40 71.47, 11.02, 1.13

 

TABLE 17 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.2(m, OOC—CH),3.3-4.1(m, alkyl- O—CH₂, alkyl-O—CH, N⁺—CH₃, N⁺—CH₂, phe-O—CH₂, COO—CH₂), 4.6(m, BO—CH₂), 6.9, 7.8(bs, phe-H) Compound Elemental analysis (C%, H %, N %) No. x y MW Found values Calculated values 64 0.9 0.1 18200071.88, 10.20, 0.44 72.01, 10.19, 0.25 65 0.7 0.3 191000 70.53, 10.70,0.83 70.75, 10.49, 0.71 66 0.5 0.5 208000 69.95, 10.50, 1.39 69.67,10.74, 1.10

 

TABLE 18 Structure of boric diester compound

¹HNMR (δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 3.3- 4.1(m,alkyl-O—CH₂, alkyl-O— CH, N⁺—CH₃, N⁺—CH₂, phe-O— CH₂, COO—CH₂), 4.6(m,BO— CH₂), 6.9, 7.8(bs, phe-H) Compound Elemental analysis (C %, H %, N%) No. x y MW Found values Calculated values 67 0.9 0.1 712000 72.51,10.00, 0.51 72.34, 10.29, 0.25 68 0.7 0.3 754000 71.29, 10.57, 0.8171.10, 10.57, 0.69 69 0.5 0.5 832000 70.10, 10.61, 1.33 70.02, 10.82,1.07

 

TABLE 19 Structure of boric diester compound

¹HNMR(δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 3.3-3.9 (m, alkyl-O—CH₂,alkyl-O—CH, N⁺—CH₃, N⁺—CH₂, Com- phe-O—CH₂), 4.6(m, BO—CH₂), 6.9,7.8(bs, phe-H) pound Elemental analysis (C %, H %, N %) No. x y MW Foundvalues Calculated values 70 0.9 0.1 4180000 72.20, 10.41, 0.50 72.16,10.58, 0.26 71 0.7 0.3 4440000 71.58, 11.23, 1.00 71.67, 10.96, 0.72 720.5 0.5 4720000 71.25, 11.41, 1.40 71.23, 11.30, 1.12

 

TABLE 20 Structure of boric diester compound

¹HNMR(δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.6(m, phe-CH),3.3-4.1(m, alkyl-O—CH₂, alkyl-O—CH, N⁺—CH₃, N⁺—CH₂, phe-O—CH₂, COO—CH₂),4.6(m, phe-CH₂, Com- BO—CH₂), 6.9, 7.8(bs, phe-H) pound Elementalanalysis (C %, H %, N %) No. x y MW Found values Calculated values 730.9 0.1 280000 72.80, 10.36, 0.31 72.93, 10.29, 0.25 74 0.7 0.3 35600072.81, 10.72, 0.99 72.73, 10.55, 0.69 75 0.5 0.5 312000 72.51, 10.70,1.37 72.56, 10.78, 1.07

 

TABLE 21 Structure of boric diester compound

¹HNMR(δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.2-2.6 (m, OOC—CH,phe-CH), 3.3-3.5(m, N⁺—CH₃, N⁺—CH₂, alkyl-O—CH₂), 4.0(m, COO—CH₂),4.6(m, BO—CH₂), 7.3, Com- 7.8(bs, phe-H) pound Elemental analysis (C %,H %, N %) No. x y MW Found values Calculated values 76 0.9 0.1 52800074.59, 10.43, 0.30 74.88, 10.70, 0.31 77 0.7 0.3 650000 73.61, 11.26,1.03 73.54, 11.02, 0.82 78 0.5 0.5 472000 72.38, 11.19, 1.50 72.47,11.28, 1.22

 

TABLE 22 Structure of boric diester compound

¹HNMR(δ ppm): 0.8-1.5(m, alkyl-CH₃, alkyl-CH₂), 2.6(m, phe-CH),3.3-3.5(m, N⁺—CH₃, N⁺—CH₂, alkyl-O—CH₂, Com- N—CH₂-phe), 4.6(m, BO—CH₂),7.0-7.6(bs, phe-H) pound Elemental analysis (C %, H %, N %) No. x y MWFound values Calculated values 79 0.9 0.1 419000 75.33, 10.84, 0.6175.63, 10.70, 0.31 80 0.7 0.3 360000 75.32, 10.89, 1.10 75.55, 11.02,0.81 81 0.5 0.5 527000 75.37, 11.46, 1.21 75.48, 11.28, 1.21

 

TABLE 23 Abbreviation Structure of fat-soluble anion salt TFPB

TCPB

DESS

 

The amounts of boric diester compound or onium salt compound used inthese examples are expressed in terms of parts by weight of the boricdiester compound or the onium salt compound per 100 parts by weight ofthe combined amount of the boric diester compound and the onium saltcompound. Where a polymer is added to these compounds, they areexpressed in terms of parts by weight of the boric diester compound orthe onium salt compound per 100 parts by weight of the combined amountof the boric diester compound, the onium salt compound and the polymer.The amount of fat-soluble anion salt used is expressed as its molarratio based on the onium salt compound [i.e., (the number of moles ofthe fat-soluble anion salt)/(the number of moles of the onium saltcompound)].

In these examples, the term “slope” refers to the value of s in thefollowing equation (Nernst equation), and indicates the change inmembrane potential (mV) which occurs when the concentration of the ionicspecies to be determined (i.e., hydrogencarbonate ion) is altered from10⁻³ M to 10⁻² M.

E _(i) =E _(i) ⁰ −s log(a _(i))

wherein E_(i) ⁰ is the electric potential observed when a molecularspecies (i) having an activity a_(i) is absent, E_(i) is the electricpotential observed when the molecular species (i) having an activitya_(i) is present, and s is the slope.

The hydrogencarbonate ion selectivity coefficients (K_(HCO) ₃ _(,X))relative to various ions were determined according to the followingequation.

${\log \quad K_{{HCO}_{3},X}} = \frac{E_{X} - E_{{HCO}_{3}}}{- s}$

 

wherein K_(HCO) ₃ _(,X) is the hydrogencarbonate ion selectivitycoefficient relative to an ion X, E_(X) is the electric potential forthe interfering ionic species, E_(HCO) ₃ is the electric potential forhydrogencarbonate ion, and s is the slope.

The following preparation examples are concerned with the preparation ofseveral typical ones of the onium salt compounds and aromatic boricdiesters listed in the foregoing Tables 1 to 22. Other compounds thanthose described in the preparation examples may be synthesized insubstantially the same manner as in the preparation examples.

Preparation Example 1

(Compound No. 36)

2.99 g (10.4 mmol) of 4-(2-ethylhexyloxy)bromobenzene was suspended in50 ml of tetrahydrofuran. After this suspension was cooled to −70° C., asolution of n-butyllithium (20.9 mmol) in hexane was slowly addeddropwise thereto. After the reaction mixture was stirred at −70° C. for30 minutes, 21.7 g (209 mmol) of trimethoxyborane was slowly addeddropwise thereto. After the stirring was continued at −70° C. for 1hour, the reaction mixture was slowly heated to ordinary temperature andthen stirred at ordinary temperature for 2 hours. Moreover, afterhydrochloric acid was added to the reaction mixture so as to adjust itspH to a value of 1 or less, and the reaction mixture was stirred atordinary temperature for 20 hours, water and ether were added theretoand the organic layer was separated. The solvent was evaporated underreduced pressure to obtain 3 g of a pale-yellow oily material.

3 g of the resulting pale-yellow oily material was dissolved in 100 mlof toluene, and this solution was mixed with 30 ml of an aqueoussolution containing 1 g of polyvinyl alcohol (with a degree ofpolymerization of 2,000). Using a Dean-Stark trap, this mixture washeated under reflux so that the water contained in the system might beremoved by azeotropic distillation. After completion of the reaction,the toluene was evaporated under reduced pressure. The residue waspassed through a silica gel column (with chloroform) to obtain 1.2 g ofa white solid. When the purified product was subjected to ¹HNMRspectroscopy [in CDCl₃ by using TMS as a standard (0.00 ppm)], thefollowing results were obtained.

¹HNMR: 7.7 ppm (bs; 2H, Phe-H), 6.9 ppm (bs; 2H, Phe-H), 4.6-4.7 ppm (m;2H, —O—CH<), 3.8 ppm (bs; 2H, Phe-O—CH₂), 2.5-0.7 (m; 19H, CH, CH₂, CH₃)

IR (KBr method): 1376 cm⁻¹ (B-O stretching vibrations).

Average molecular weight determined by gel permeation chromatography:330,000.

Preparation Example 2

(Compound No. 39)

In the same manner as in Preparation Example 1, a pale-yellow oilymaterial was obtained by reacting 4-(octadecyloxy)bromobenzene withtrimethoxyborane in the presence of n-butyllithium. Then, a boricdiester compound was synthesized from the above pale-yellow oilymaterial and polyvinyl alcohol in the same manner as in PreparationExample 1. When the purified product was subjected to ¹HNMR spectroscopy[in CDCl₃ by using TMS as a standard (0.00 ppm)], the following resultswere obtained.

¹HNMR: 7.7 ppm (bs; 2H, Phe-H), 6.9 ppm (bs; 2H, Phe-H), 4.6-4.7 ppm (m;2H, —O—CH<), 3.8 ppm (bs; 2H, Phe-O—CH₂), 2.5-0.7 (m; 39H, CH, CH₂, CH₃)

IR (KBr method): 1376 cm⁻¹ (B-O stretching vibrations).

Average molecular weight determined by gel permeation chromatography:534,000.

Example 1

(Formation of Membrane Nos. 1-174)

The onium salt compounds, boric diester compounds and optional polymersshown in Tables 24-31 were used in the respective amounts indicated inTables 24-31. For each Membrane No., these ingredients were dissolved in2.5 ml of tetrahydrofuran, and the resulting solution was cast in aPetri dish made of glass and having a diameter of 27 mm. A membranousmaterial was obtained by evaporating the solvent at 20° C. underatmospheric pressure for 24 hours and then drying the residue in avacuum of 1 mmHg for 5 hours. The state of dispersion in the membranesthus obtained is also shown in Tables 24-31.

TABLE 24 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention  1  1 0.16 0.11 23100.0 66.0 PVC 50.0 Uniformly dispersed 50.2 0.07 0.01 0.55  2  1 8.15.12 23 100.0 63.3 PVC 50.0 Uniformly dispersed 58.3 0.03 0.01 0.67  3 1 40.5 21.3 23 100.0 52.5 PVC 50.0 Uniformly dispersed 43.5 0.12 0.070.63  4  2 22.2 12.9 23 100.0 58.1 PVC 50.0 Uniformly dispersed 47.90.05 0.03 0.43  5  2 22.2 12.9 23 100.0 58.1 PVdC 50.0 Uniformlydispersed 50.9 0.05 0.02 0.43  6  2 2.2 1.73 23 100.0 78.6 PVdC 25.0Uniformly dispersed 45.8 0.07 0.01 0.55  7  3 22.2 12.9 23 100.0 57.8PVC 50.0 Uniformly dispersed 51.3 0.07 0.03 0.53  8  4 0.16 0.11 23100.0 66.6 PVC 50.0 Uniformly dispersed 46.5 0.06 0.02 0.40  9  4 8.05.06 23 100.0 63.3 PVC 50.0 Uniformly dispersed 46.6 0.06 0.02 0.52 10 4 32.0 17.6 23 100.0 54.9 PVC 50.0 Uniformly dispersed 46.6 0.13 0.060.73 11  5 11.7 7.23 23 100.0 62.0 PVC 50.0 Uniformly dispersed 51.20.05 0.02 0.61 12  6 14.0 8.53 23 100.0 61.0 PVC 50.0 Uniformlydispersed 50.5 0.04 0.02 0.77 13  7 17.8 10.6 23 100.0 59.6 PVC 50.0Uniformly dispersed 49.5 0.05 0.02 0.67 14  8 0.73 0.48 23 100.0 66.3PVC 50.0 Uniformly dispersed 46.8 0.05 0.01 0.72 15  8 7.3 4.64 23 100.063.6 PVC 50.0 Uniformly dispersed 53.5 0.07 0.02 0.73 16  8 36.5 19.6 23100.0 53.6 PVC 50.0 Uniformly dispersed 55.5 0.10 0.02 0.63 17  9 19.211.3 23 100.0 59.1 PVC 50.0 Uniformly dispersed 55.2 0.06 0.01 0.46 1810 50.0 33.3 23 100.0 66.7 — — Uniformly dispersed 49.9 0.06 0.01 0.5219 10 75.0 50.0 23  75.0 50.0 — — Uniformly dispersed 53.3 0.06 0.010.48 20 10 100.0 66.7 23  50.0 33.3 — — Uniformly dispersed 57.7 0.070.03 0.48 21 11 50.0 33.3 23 100.0 66.7 — — Uniformly dispersed 46.90.05 0.01 0.50 22 12 100.0 66.7 23  50.0 33.3 — — Uniformly dispersed48.3 0.07 0.02 0.49 *pbw = part by weight

 

TABLE 25 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 23 12 115.0 76.7 23 35.0 23.3 — — Uniformly dispersed 46.5 0.06 0.01 0.58 24 12 125.0 71.823  49.0 28.2 — — Uniformly dispersed 51.4 0.04 0.01 0.41 25 13 50.033.3 23 100.0 66.7 — — Uniformly dispersed 55.5 0.04 0.03 0.43 26  1 8.15.12 24 100.0 63.3 PVC 50.0 Uniformly dispersed 49.5 0.04 0.01 0.64 27 1 8.1 5.12 25 100.0 63.3 PVC 50.0 Uniformly dispersed 48.2 0.06 0.010.50 28  1 8.1 5.12 26 100.0 63.3 PVdC 50.0 Uniformly dispersed 51.30.05 0.03 0.58 29  1 8.1 5.12 27 100.0 63.3 PVdC 50.0 Uniformlydispersed 53.8 0.05 0.02 0.75 30  1 8.1 5.12 28 100.0 63.3 PVdC 50.0Uniformly dispersed 48.9 0.06 0.03 0.56 31  1 8.1 5.12 29 100.0 63.3PVdC 50.0 Uniformly dispersed 44.7 0.06 0.03 0.66 32  1 8.1 5.12 34150.0 63.3 — — Uniformly dispersed 46.7 0.07 0.03 0.63 33  1 8.1 5.12 35150.0 63.3 — — Uniformly dispersed 45.1 0.05 0.01 0.47 34  2 11.0 6.8325 100.0 62.1 PVdC 50.0 Uniformly dispersed 51.0 0.04 0.01 0.54 35  322.2 12.9 28 100.0 58.1 PVdC 50.0 Uniformly dispersed 52.4 0.05 0.010.69 36  4 16.0 9.64 26 100.0 60.2 PVdC 50.0 Uniformly dispersed 49.00.07 0.02 0.63 37  4 16.0 9.64 28 100.0 60.2 PVdC 50.0 Uniformlydispersed 54.0 0.07 0.03 0.52 38  4 16.0 9.64 35 150.0 60.2 — —Uniformly dispersed 51.4 0.06 0.01 0.73 39  5 11.7 7.23 27 100.0 61.8PVdC 50.0 Uniformly dispersed 51.6 0.05 0.03 0.63 40  6 14.0 8.53 27100.0 61.0 PVdC 50.0 Uniformly dispersed 45.3 0.06 0.03 0.59 41  7 17.910.7 29 100.0 59.6 PVdC 50.0 Uniformly dispersed 43.9 0.04 0.01 0.59 42 8 0.7 0.46 24 100.0 66.4 PVC 50.0 Uniformly dispersed 51.6 0.04 0.030.71 43  8 7.3 4.64 25 100.0 63.6 PVC 50.0 Uniformly dispersed 54.7 0.050.03 0.61 44  8 16.6 10.0 28 100.0 60.0 PVC 50.0 Uniformly dispersed46.2 0.05 0.01 0.50 45  8 33.5 19.9 29  84.5 50.3 PVdC 50.0 Uniformlydispersed 49.8 0.05 0.01 0.57 46  8 7.3 4.64 34 150.0 95.3 — — Uniformlydispersed 56.3 0.18 0.07 0.65 *pbw = part by weight

 

TABLE 26 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 47  9 19.2 5.44 27100.0 59.1 PVC 50.0 Uniformly dispersed 51.2 0.06 0.02 0.58 48 10 10.29.26 25 100.0 90.7 — — Uniformly dispersed 52.2 0.15 0.08 0.61 49 1020.3 14.0 35 125.0 86.0 — — Uniformly dispersed 48.3 0.14 0.07 0.71 5011 49.1 32.9 27 100.0 67.1 — — Uniformly dispersed 46.9 0.05 0.01 0.5351 11 18.3 11.6 35 140.0 81.7 — — Uniformly dispersed 53.6 0.17 0.060.82 52 12 75.0 42.9 24 100.0 57.1 — — Uniformly dispersed 51.7 0.040.01 0.67 53 12 75.0 42.9 26 100.0 57.1 — — Uniformly dispersed 47.40.06 0.03 0.66 54 12 75.0 42.9 28 100.0 57.1 — — Uniformly dispersed45.8 0.06 0.02 0.48 55 12 75.0 42.9 29 100.0 57.1 — — Uniformlydispersed 44.4 0.05 0.03 0.70 56 12 75.0 42.9 34 100.0 57.1 — —Uniformly dispersed 47.4 0.06 0.02 0.69 57 13 75.0 42.9 24 100.0 57.1 —— Uniformly dispersed 46.5 0.04 0.01 0.50 58 13 75.0 42.9 28 100.0 57.1— — Uniformly dispersed 57.1 0.05 0.03 0.53 59 13 75.0 42.9 34 100.057.1 — — Uniformly dispersed 53.7 0.05 0.03 0.49 60 13 75.0 42.9 35100.0 57.1 — — Uniformly dispersed 56.6 0.05 0.02 0.57 61 14 10.5 6.5 23100.0 62.3 PVC 50.0 Uniformly dispersed 51.3 0.07 0.02 0.78 62 14 31.317.3 23 100.0 55.2 PVC 50.0 Uniformly dispersed 49.5 0.07 0.01 0.86 6315 5.3 3.4 23 100.0 64.4 PVC 50.0 Uniformly dispersed 56.0 0.06 0.030.46 64 15 43.2 22.4 23 100.0 51.8 PVC 50.0 Uniformly dispersed 52.00.09 0.01 0.59 65 16 0.10 0.07 23 100.0 66.6 PVC 50.0 Uniformlydispersed 50.5 0.04 0.01 0.81 66 16 28.6 16.0 23 100.0 56.0 PVC 50.0Uniformly dispersed 47.1 0.05 0.02 0.59 67 17 10.3 6.4 23 100.0 62.4 PVC50.0 Uniformly dispersed 47.1 0.08 0.02 0.61 68 17 25.5 14.5 23 100.057.0 PVC 50.0 Uniformly dispersed 54.4 0.06 0.01 0.74 69 18 1.36 0.90 23100.0 66.1 PVC 50.0 Uniformly dispersed 56.9 0.07 0.02 0.77 *pbw = partby weight

 

TABLE 27 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 70 18 22.8 13.2 23100.0 57.9 PVC 50.0 Uniformly dispersed 54.1 0.06 0.01 0.67 71 19 1.500.99 23 100.0 66.0 PVC 50.0 Uniformly dispersed 50.0 0.07 0.02 0.71 7219 8.35 5.3 23 100.0 63.2 PVC 50.0 Uniformly dispersed 49.3 0.05 0.010.64 73 20 3.68 2.4 23 100.0 65.1 PVC 50.0 Uniformly dispersed 54.2 0.060.01 0.72 74 20 20.4 12.0 23 100.0 58.7 PVC 50.0 Uniformly dispersed55.5 0.06 0.02 0.80 75 21 25.9 14.7 23 100.0 56.9 PVC 50.0 Uniformlydispersed 47.6 0.07 0.01 0.60 76 21 57.3 27.6 23 100.0 48.2 PVC 50.0Uniformly dispersed 58.0 0.05 0.02 0.73 77 22 21.7 12.6 23 100.0 58.2PVC 50.0 Uniformly dispersed 49.3 0.08 0.02 0.74 78 22 65.4 30.4 23100.0 46.4 PVC 50.0 Uniformly dispersed 51.2 0.07 0.01 0.59 79 14 46.523.7 24 100.0 50.9 PVC 50.0 Uniformly dispersed 46.5 0.08 0.03 0.81 8015 13.2 8.1 24 100.0 61.3 PVC 50.0 Uniformly dispersed 54.4 0.05 0.020.67 81 16 10.5 6.5 25 100.0 62.3 PVC 50.0 Uniformly dispersed 54.6 0.040.01 0.62 82 17 10.5 6.5 25 100.0 62.3 PVC 50.0 Uniformly dispersed 49.90.08 0.01 0.64 83 18 10.5 6.5 26 100.0 62.3 PVC 50.0 Uniformly dispersed57.2 0.07 0.02 0.75 84 19 10.5 6.5 26 100.0 62.3 PVC 50.0 Uniformlydispersed 48.8 0.06 0.01 0.81 85 20 10.5 6.5 27 100.0 62.3 PVC 50.0Uniformly dispersed 52.3 0.06 0.01 0.87 86 21 45.0 23.1 27 100.0 51.3PVC 50.0 Uniformly dispersed 52.0 0.07 0.01 0.84 87 22 45.0 23.1 28100.0 51.3 PVC 50.0 Uniformly dispersed 51.1 0.04 0.02 0.64 88 14 46.523.7 28 100.0 50.9 PVC 50.0 Uniformly dispersed 56.3 0.09 0.02 0.62 8915 13.2 8.1 29 100.0 61.3 PVC 50.0 Uniformly dispersed 49.5 0.05 0.010.71 90 16 10.5 6.5 29 100.0 62.3 PVC 50.0 Uniformly dispersed 52.2 0.060.01 0.76 91 17 10.5 6.5 30 100.0 62.3 PVC 50.0 Uniformly dispersed 54.60.06 0.01 0.58 92 18 10.5 6.5 30 100.0 62.3 PVC 50.0 Uniformly dispersed47.6 0.07 0.01 0.57 93 19 10.5 6.5 31 100.0 62.3 PVC 50.0 Uniformlydispersed 53.3 0.04 0.01 0.62 *pbw = part by weight

 

TABLE 28 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention  94 20 10.5 6.5 31100.0 62.3 PVC 50.0 Uniformly dispersed 54.1 0.06 0.01 0.67  95 21 35.018.9 32 100.0 54.1 PVC 50.0 Uniformly dispersed 47.9 0.07 0.01 0.70  9622 35.0 18.9 32 100.0 54.1 PVC 50.0 Uniformly dispersed 55.5 0.06 0.020.65  97 14 45.0 23.1 33 100.0 51.3 PVC 50.0 Uniformly dispersed 56.20.07 0.02 0.81  98 15 45.0 23.1 33 100.0 51.3 PVC 50.0 Uniformlydispersed 52.0 0.06 0.01 0.74  99  1 8.1 7.5 36 100.0 92.5 — — Uniformlydispersed 57.3 0.05 0.01 0.65 100  1 32.4 24.5 36 100.0 75.5 — —Uniformly dispersed 48.9 0.06 0.01 0.69 101  3 22.2 18.2 36 100.0 81.8 —— Uniformly dispersed 46.6 0.05 0.02 0.63 102  3 44.4 30.7 36 100.0 69.3— — Uniformly dispersed 54.1 0.05 0.01 0.78 103 11 18.3 15.5 36 100.084.5 — — Uniformly dispersed 54.7 0.06 0.01 0.84 104 11 50.0 33.3 36100.0 66.7 — — Uniformly dispersed 49.9 0.06 0.01 0.64 105 12 50.0 33.336 100.0 66.7 — — Uniformly dispersed 56.9 0.05 0.02 0.79 106 12 80.044.4 36 100.0 55.6 — — Uniformly dispersed 55.2 0.05 0.01 0.61 107 1450.0 33.3 36 100.0 66.7 — — Uniformly dispersed 54.6 0.07 0.01 0.77 10814 80.0 44.4 36 100.0 55.6 — — Uniformly dispersed 49.7 0.06 0.01 0.77109 15 50.0 33.3 36 100.0 66.7 — — Uniformly dispersed 44.4 0.06 0.020.65 110 15 80.0 44.4 36 100.0 55.6 — — Uniformly dispersed 52.1 0.060.01 0.64 111  5 11.7 10.5 37 100.0 89.5 — — Uniformly dispersed 49.70.07 0.02 0.85 112  7 17.9 15.2 37 100.0 84.8 — — Uniformly dispersed56.3 0.05 0.02 0.70 113  8 0.7 0.7 38 100.0 99.3 — — Uniformly dispersed51.0 0.05 0.01 0.63 114 10 10.2 9.3 38 100.0 90.7 — — Uniformlydispersed 57.4 0.07 0.01 0.70 115  1 8.1 7.5 39 100.0 92.5 — — Uniformlydispersed 45.9 0.07 0.01 0.80 116  1 24.3 19.5 39 100.0 80.5 — —Uniformly dispersed 54.5 0.06 0.01 0.75 *pbw = part by weight

 

TABLE 29 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 117  5 11.7 10.5 39100.0 89.5 — — Uniformly dispersed 52.3 0.06 0.01 0.64 118  5 33.5 25.139 100.0 74.9 — — Uniformly dispersed 54.4 0.06 0.01 0.68 119  8 7.3 6.839 100.0 93.2 — — Uniformly dispersed 49.8 0.05 0.02 0.67 120  8 33.525.1 39 100.0 74.9 — — Uniformly dispersed 56.0 0.07 0.01 0.72 121  919.2 16.1 39 100.0 83.9 — — Uniformly dispersed 54.1 0.06 0.01 0.74 122 9 35.0 25.9 39 100.0 74.1 — — Uniformly dispersed 55.7 0.06 0.01 0.68123 11 18.3 15.5 39 100.0 84.5 — — Uniformly dispersed 58.0 0.06 0.020.78 124 11 50.0 33.3 39 100.0 66.7 — — Uniformly dispersed 49.7 0.070.01 0.65 125 12 30.0 23.1 39 100.0 76.9 — — Uniformly dispersed 49.70.06 0.01 0.82 126 12 80.0 44.4 39 100.0 55.6 — — Uniformly dispersed52.3 0.06 0.02 0.63 127 13 30.0 23.1 39 100.0 76.9 — — Uniformlydispersed 55.5 0.07 0.02 0.79 128 13 80.0 44.4 39 100.0 55.6 — —Uniformly dispersed 54.6 0.04 0.01 0.58 129 18 1.6 1.6 39 100.0 98.4 — —Uniformly dispersed 48.6 0.06 0.01 0.77 130 18 8.9 8.2 39 100.0 91.8 — —Uniformly dispersed 56.6 0.04 0.01 0.66 131 20 3.2 3.1 39 100.0 96.9 — —Uniformly dispersed 47.8 0.07 0.02 0.68 132 20 21.5 17.7 39 100.0 82.3 —— Uniformly dispersed 54.3 0.06 0.01 0.74 133 40 150.0 100.0 — — — — —Uniformly dispersed 56.1 0.04 0.01 0.35 134 41 150.0 100.0 — — — — —Uniformly dispersed 49.2 0.05 0.02 0.45 135 42 150.0 100.0 — — — — —Uniformly dispersed 47.8 0.03 0.02 0.40 136 43 150.0 100.0 — — — — —Uniformly dispersed 56.6 0.04 0.01 0.38 137 44 150.0 100.0 — — — — —Uniformly dispersed 56.2 0.06 0.01 0.42 138 45 150.0 100.0 — — — — —Uniformly dispersed 49.5 0.03 0.02 0.40 139 46 150.0 100.0 — — — — —Uniformly dispersed 52.7 0.02 0.01 0.31 *pbw = part by weight

 

TABLE 30 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 140 47 150.0 100.0 —— — — — Uniformly dispersed 55.4 0.04 0.01 0.38 141 48 150.0 100.0 — — —— — Uniformly dispersed 54.6 0.04 0.02 0.45 142 49 150.0 100.0 — — — — —Uniformly dispersed 49.9 0.02 0.01 0.34 143 50 150.0 100.0 — — — — —Uniformly dispersed 55.2 0.02 0.01 0.41 144 51 150.0 100.0 — — — — —Uniformly dispersed 57.3 0.05 0.02 0.41 145 52 150.0 100.0 — — — — —Uniformly dispersed 49.7 0.03 0.01 0.30 146 53 150.0 100.0 — — — — —Uniformly dispersed 57.0 0.03 0.01 0.37 147 54 150.0 100.0 — — — — —Uniformly dispersed 54.0 0.05 0.02 0.37 148 55 150.0 100.0 — — — — —Uniformly dispersed 48.8 0.03 0.01 0.30 149 56 150.0 100.0 — — — — —Uniformly dispersed 50.1 0.03 0.01 0.42 150 57 150.0 100.0 — — — — —Uniformly dispersed 54.6 0.05 0.02 0.54 151 58 150.0 100.0 — — — — —Uniformly dispersed 54.5 0.04 0.01 0.32 152 59 150.0 100.0 — — — — —Uniformly dispersed 47.9 0.04 0.01 0.40 153 60 150.0 100.0 — — — — —Uniformly dispersed 56.3 0.05 0.02 0.40 154 61 150.0 100.0 — — — — —Uniformly dispersed 54.8 0.03 0.01 0.35 155 62 150.0 100.0 — — — — —Uniformly dispersed 57.2 0.03 0.02 0.40 156 63 150.0 100.0 — — — — —Uniformly dispersed 48.2 0.05 0.02 0.40 157 64 150.0 100.0 — — — — —Uniformly dispersed 56.9 0.03 0.01 0.33 158 65 150.0 100.0 — — — — —Uniformly dispersed 54.6 0.03 0.01 0.42 159 66 150.0 100.0 — — — — —Uniformly dispersed 54.6 0.05 0.02 0.42 160 67 150.0 100.0 — — — — —Uniformly dispersed 52.9 0.03 0.01 0.37 161 68 150.0 100.0 — — — — —Uniformly dispersed 54.8 0.04 0.02 0.48 162 69 150.0 100.0 — — — — —Uniformly dispersed 56.7 0.05 0.02 0.52 *pbw = part by weight

 

TABLE 31 Onium salt compound Boric diester compound Composi- Composi-Selectivity Com- tional Com- tional Polymer coefficients Membrane poundWeight ratio pound Weight ratio Desig- Weight State of dispersion Sloperelative to anions No. No. (mg) (pbw*) No. (mg) (pbw*) nation (mg) inmembrane (mV/dec) NO₃ ⁻ Cl⁻ SaI⁻ Present invention 163 70 150.0 100.0 —— — — — Uniformly dispersed 54.1 0.03 0.01 0.40 164 71 150.0 100.0 — — —— — Uniformly dispersed 54.1 0.03 0.01 0.39 165 72 150.0 100.0 — — — — —Uniformly dispersed 56.9 0.04 0.02 0.46 166 73 150.0 100.0 — — — — —Uniformly dispersed 53.4 0.03 0.01 0.32 167 74 150.0 100.0 — — — — —Uniformly dispersed 54.7 0.04 0.02 0.40 168 75 150.0 100.0 — — — — —Uniformly dispersed 49.7 0.04 0.02 0.56 169 76 150.0 100.0 — — — — —Uniformly dispersed 56.2 0.03 0.01 0.32 170 77 150.0 100.0 — — — — —Uniformly dispersed 54.8 0.04 0.01 0.41 171 78 150.0 100.0 — — — — —Uniformly dispersed 55.0 0.04 0.02 0.41 172 79 150.0 100.0 — — — — —Uniformly dispersed 49.0 0.03 0.01 0.38 173 80 150.0 100.0 — — — — —Uniformly dispersed 46.8 0.04 0.02 0.40 174 81 150.0 100.0 — — — — —Uniformly dispersed 47.7 0.04 0.02 0.47 Comparative Examples Comparative— — — 23 100.0 66.7 PVC 50.0 Uniformly dispersed 10.6 — — — Membrane 1Comparative TOAB 10.0 5.55 — — — PVC 50.0 Uniformly dispersed 50.4 36.90.04 308.4 Membrane 2 Comparative TOTC 5.0 3.16 — — — PVC 50.0 Uniformlydispersed 57.9 — 19.95 — Membrane 3 Comparative TOABr 22.2 12.9 — — —PVC 50.0 Uniformly dispersed 56.3 25.1 10.0 — Membrane 4 *pbw = part byweight

 

Each of the membranous materials thus obtained was attached to anelectrode as illustrated in FIG. 1. Then, using an apparatus asillustrated in FIG. 2, the relationship between ion concentration andelectric potential difference at room temperature was measured forvarious anions. On the basis of the results thus obtained, thehydrogencarbonate ion selectivity coefficients relative to those anionswere determined according to a well-known method [i.e., the methoddescribed in G. J. Moody and J. D. Thomas (transl. by Shin Munemori andKazuo Hiuro), “Ion-selective Electrodes”, Kyoritsu Shuppan, p. 18(1977)]. The results thus obtained are also shown in Tables 24-31.

Comparative Example 1

(Formation of Comparative Membrane 1)

Using 50 mg of PVC (with a degree of polymerization of 1,000) and 100 mgof a boric diester compound (Compound No. 14), a membranous material wasobtained in exactly the same manner as in Example 1. The state ofdispersion in this membrane is also shown in Table 31. Using themembranous material thus obtained, its hydrogencarbonate ion selectivitycoefficients relative to various anions were determined in the samemanner as in Example 1. The results thus obtained are also shown inTables 31. In the tables, a dash (-) indicates that no addition was madeor no value was calculable.

Comparative Example 2

(Formation of Comparative Membrane 2)

Using 10 mg of tetraoctylammonium bromide (TOABr), 20 mg of4-(n-decyl)-1-trifluoroacetylbenzene, 50 mg of PVC (with a degree ofpolymerization of 1,000), and 100 mg of di(2-ethylhexyl)sebacate(manufactured by Kanto Chemical Co., Inc.), a membranous material wasobtained in exactly the same manner as in Example 1. The state ofdispersion in this membrane is also shown in Table 31. Using themembranous material thus obtained, its hydrogencarbonate ion selectivitycoefficients relative to various anions were determined in the samemanner as in Example 1. The results thus obtained are also shown inTables 31.

Comparative Example 3

(Formation of Comparative Membrane 3)

Using 5 mg of trioctyltin chloride (TOTC), 3 mg of4-(n-decyl)-1-trifluoroacetylbenzene, 50 mg of PVC (with a degree ofpolymerization of 1,000), and 100 mg of di(2-ethylhexyl)sebacate, amembranous material was obtained in exactly the same manner as inExample 1. The state of dispersion in this membrane is also shown inTable 31. Using the membranous material thus obtained, itshydrogencarbonate ion selectivity coefficients relative to variousanions were determined in the same manner as in Example 1. The resultsthus obtained are also shown in Tables 31.

Comparative Example 4

(Formation of Comparative Membrane 4)

Using 50 mg of PVC (with a degree of polymerization of 1,000), 100 mg ofo-nitrophenyl octyl ether, and tetraoctadecylammonium bromide (TOAB), amembranous material was obtained in exactly the same manner as inExample 1. The state of dispersion in this membrane is also shown inTable 31. Using the membranous material thus obtained, itshydrogencarbonate ion selectivity coefficients relative to variousanions were determined in the same manner as in Example 1. The resultsthus obtained are also shown in Tables 31.

The ion selectivity coefficients shown in the examples indicate that thehydrogencarbonate ion selectivity of the anion-sensitive membrane isbetter as their values become smaller. As is evident from Tables 24-31,the anion-selective electrodes using the bicarbonate ion-sensitivemembrane of the present invention have excellent hydrogencarbonate ionselectivity relative to nitrate, chloride and salicylate ions present inbiological fluids, and can hence measure the hydrogencarbonate ionconcentrations in biological fluids accurately.

On the other hand, the membrane composed of a boric diester and PVC(Comparative Membrane 1) is not sensitive to hydrogencarbonate ion atall, and cannot measure hydrogencarbonate ion concentrations. Moreover,the membrane composed of a quaternary ammonium salt, a4-alkyl-1-trifluoroacetylbenzene, a polymer and a plasticizer(Comparative Membrane 2), the membrane composed of trioctyltin chloride,a 4-alkyl-1-trifluoroacetylbenzene, a polymer and a plasticizer(Comparative Membrane 3), and the membrane composed of a quaternaryammonium salt, NPOE, and a polymer (Comparative Membrane 4) haveinsufficient hydrogencarbonate ion selectivity relative to nitrate,salicylate or chloride ion, so that it is difficut to measure thehydrogencarbonate ion concentrations in biological fluids accurately byusing these membranes.

Example 2

(Formation of Membrane Nos. 175-197)

The onium salt compounds and fat-soluble anion salts shown in Table 32were used in the respective amounts indicated in Table 32. For eachMembrane No., the indicated amounts of the onium salt compound andfat-soluble anion salt, 50 mg of PVC (with a degree of polymerization of1,000), and 100 mg of a boric diester compound (Compound No. 23) weredissolved in 2.5 ml of tetrahydrofuran, and the resulting solution wascast in a Petri dish made of glass and having a diameter of 27 mm. Amembranous material was obtained by evaporating the solvent at 20° C.under atmospheric pressure for 24 hours. The state of dispersion in themembranes thus obtained is also shown in Table 32.

TABLE 32 Onium salt compound Composi- Fat-soluble anion Selectivity Com-tional Com- Response coefficients Membrane pound Weight ratio poundWeight Molar State of dispersion Slope speed relative to anions No. No.(mg) (pbw*) No. (mg) ratio in membrane (mV/dec) (seconds) NO₃ ⁻ Cl⁻ SaI⁻Present invention 175  1 8.1 5.12 TFPB 0.9 0.05 Uniformly dispersed 41.326 0.03 0.01 0.60 176  1 8.1 5.12 TFPB 1.8 0.10 Uniformly dispersed 38.920 0.04 0.01 0.58 177  1 8.1 5.12 TFPB 3.6 0.20 Uniformly dispersed 42.510 0.06 0.02 0.67 178  1 8.1 5.12 TFPB 7.2 0.40 Uniformly dispersed 45.6 9 0.05 0.01 0.77 179  8 7.3 4.64 TFPB 0.9 0.05 Uniformly dispersed 51.342 0.05 0.01 0.73 180  8 7.3 4.64 TFPB 1.8 0.10 Uniformly dispersed 50.625 0.06 0.03 0.61 181  8 7.3 4.64 TFPB 3.6 0.20 Uniformly dispersed 48.5 9 0.04 0.01 0.58 182  8 7.3 4.64 TFPB 7.2 0.40 Uniformly dispersed 38.6 9 0.05 0.02 0.55 183 12 15.9 9.58 TFPB 0.9 0.05 Uniformly dispersed52.0 21 0.06 0.01 0.57 184 12 15.9 9.58 TFPB 1.8 0.10 Uniformlydispersed 51.3 18 0.05 0.03 0.61 185 12 15.9 9.58 TFPB 3.6 0.20Uniformly dispersed 43.2 10 0.05 0.02 0.63 186 12 15.9 9.58 TFPB 7.20.40 Uniformly dispersed 44.4 10 0.04 0.03 0.49 187  1 8.1 5.12 DESS 0.40.10 Uniformly dispersed 46.9 12 0.04 0.03 0.65 188  1 8.1 5.12 TCPB 3.00.30 Uniformly dispersed 40.5 15 0.07 0.02 0.72 189  8 7.3 4.64 DESS 0.40.10 Uniformly dispersed 45.3 17 0.07 0.03 0.62 190  8 7.3 4.64 TCPB 3.00.30 Uniformly dispersed 40.8  7 0.05 0.01 0.62 191 12 15.9 9.58 DESS0.4 0.10 Uniformly dispersed 49.6 19 0.05 0.03 0.57 192 12 15.9 9.58TCPB 3.0 0.30 Uniformly dispersed 43.1 14 0.06 0.03 0.51 193 18 22.813.2 TFPB 1.0 0.05 Uniformly dispersed 50.3 15 0.05 0.01 0.70 194 1822.8 13.2 TFPB 3.7 0.20 Uniformly dispersed 52.1  7 0.06 0.02 0.64 19518 22.8 13.2 TFPB 7.4 0.40 Uniformly dispersed 50.4  5 0.05 0.01 0.63196 20 20.4 12.0 TFPB 3.2 0.10 Uniformly dispersed 54.1  8 0.04 0.020.43 197 20 20.4 12.0 TFPB 12.8  0.40 Uniformly dispersed 55.7  5 0.040.01 0.30 *pbw = part by weight

 

The onium salt compounds and fat-soluble anion salts shown in Table 33were used in the respective amounts indicated in Table 33. For eachMembrane No., the indicated amounts of the onium salt compound andfat-soluble anion salt, and 150 mg of a boric diester compound (CompoundNo. 39) were dissolved in 2.5 ml of tetrahydrofuran, and the resultingsolution was cast in a Petri dish made of glass and having a diameter of27 mm. A membranous material was obtained by evaporating the solvent at20° C. under atmospheric pressure for 24 hours. The state of dispersionin the membranes thus obtained is also shown in Table 33.

TABLE 33 Onium salt compound Composi- Fat-soluble anion Selectivity Com-tional Com- Response coefficients Membrane pound Weight ratio poundWeight Molar State of dispersion Slope speed relative to anions No. No.(mg) (pbw*) No. (mg) ratio in membrane (mV/dec) (seconds) NO₃ ⁻ Cl⁻ SaI⁻Present invention 198  1 32.4 17.8 TFPB 3.6 0.05 Uniformly dispersed48.3 15 0.05 0.01 0.70 199  1 32.4 17.8 TFPB 7.2 0.10 Uniformlydispersed 49.5 10 0.05 0.01 0.60 200  1 32.4 17.8 TFPB 14.4  0.20Uniformly dispersed 57.0  5 0.04 0.01 0.52 201  1 32.4 17.8 TFPB 28.8 0.40 Uniformly dispersed 51.3  4 0.06 0.01 0.30 202  8 29.2 16.3 TFPB3.6 0.05 Uniformly dispersed 55.5 21 0.05 0.01 0.74 203  8 29.2 16.3TFPB 7.2 0.10 Uniformly dispersed 57.6  4 0.05 0.01 0.52 204  8 29.216.3 TFPB 14.4  0.20 Uniformly dispersed 52.2  4 0.05 0.02 0.33 205  829.2 16.3 TFPB 28.8  0.40 Uniformly dispersed 48.3  3 0.04 0.02 0.21 20612 63.6 29.8 TFPB 3.6 0.05 Uniformly dispersed 51.7 18 0.05 0.02 0.60207 12 63.6 29.8 TFPB 7.2 0.10 Uniformly dispersed 47.6 15 0.05 0.010.48 208 12 63.6 29.8 TFPB 14.4  0.20 Uniformly dispersed 50.0  4 0.040.01 0.34 209 12 63.6 29.8 TFPB 28.8  0.40 Uniformly dispersed 49.9  40.03 0.03 0.30 210  1 32.4 17.8 DESS 1.6 0.10 Uniformly dispersed 54.721 0.05 0.02 0.55 211  1 32.4 17.8 TCPB 12.0  0.30 Uniformly dispersed51.3  5 0.04 0.01 0.37 212  8 29.2 16.3 DESS 1.6 0.10 Uniformlydispersed 59.0 15 0.03 0.03 0.64 213  8 29.2 16.3 TCPB 12.0  0.30Uniformly dispersed 57.8  4 0.04 0.02 0.35 214 12 63.6 29.8 DESS 11.2 0.70 Uniformly dispersed 49.5  3 0.05 0.03 0.54 215 12 63.6 29.8 TCPB12.0  0.30 Uniformly dispersed 47.5  4 0.04 0.02 0.31 216 18 91.2 37.8TFPB 4.0 0.05 Uniformly dispersed 52.2 10 0.06 0.02 0.76 217 18 91.237.8 TFPB 14.8  0.20 Uniformly dispersed 49.6  4 0.06 0.01 0.47 218 1891.2 37.8 TFPB 29.6  0.40 Uniformly dispersed 52.3  3 0.04 0.01 0.29 21920 81.6 35.2 TFPB 12.8  0.10 Uniformly dispersed 57.4  7 0.03 0.01 0.56220 20 81.6 35.2 TFPB 51.2  0.40 Uniformly dispersed 48.5  3 0.04 0.010.25 *pbw = part by weight

 

Using the membranous materials thus obtained, their hydrogencarbonateion selectivity coefficients relative to various anions were determinedin the same manner as in Example 1. Moreover, their response speeds (99%response times) were measured by using a 10 mM solution of sodiumhydrogencarbonate as a sample. The results thus obtained are also shownin Table 33.

In Tables 32 and 33, it is evident from Membrane Nos. 175-186 and193-197 that, when tetrakis[3,5-bis(trifluoromethyl)phenyl]borate sodiumsalt, which is a fat-soluble anion salt, is added in a molar ratio of0.1 to 0.4 based on the onium salt compound, the resultinganion-selective electrode shows an increase in response speed and canhence determine hydrogencarbonate ions rapidly. Moreover, an improvementin response speed is also noted when a fat-soluble anion salt such asdi(2-ethylhexyl)sulfosuccinic acid sodium salt (DESS) ortetrakis[4-chlorophenyl]borate potassium salt (TCPB) is added (MembraneNos. 187-192). Furthermore, an improvement in response speed is alsonoted when a fat-soluble anion salt is added to a membrane using ahigh-molecular-weight boric diester in a molar ratio of 0.1 to 0.7 basedon the onium salt.

Example 3

With respect to most of the electrodes obtained in Examples 1-2 andComparative Examples 1-4, the electric potentials of each electrode whenit was immersed in a 10⁻³ M solution of sodium hydrogencarbonate andwhen it was immersed in a 10⁻² M solution of sodium hydrogencarbonatewere measured, and the absolute value of the difference therebetween wascalculated. The results thus obtained are shown in Tables 34 and 35.After these electrodes were stored in a 10⁻¹ M aqueous solution ofsodium chloride for one year, the electric potentials of each electrodewhen it was immersed in 10⁻³ M and 10⁻² M solutions of sodiumhydrogencarbonate were measured in the same manner as before, and theabsolute value of the difference therebetween was calculated. Theresults thus obtained are also shown in Tables 34 and 35. As is evidentfrom these tables, potential changes similar to those before storagewere observed even after the electrodes were stored in a 10⁻¹ M aqueoussolution of sodium chloride for one year, indicating that the electrodeshave a long life.

TABLE 34 Membrane Potential difference Potential difference No. beforeimmersion after immersion Present invention  1 50.2 46.1  2 58.3 51.3  343.5 43.8  4 47.9 44.4  5 50.9 46.7  6 45.8 45.0  7 51.3 49.9  8 46.546.0  9 46.6 46.0 10 46.6 41.5 11 51.2 50.0 12 50.5 47.2 13 49.5 47.5 1446.8 41.5 15 53.5 50.5 16 55.5 49.7 17 55.0 41.5 18 49.9 51.3 19 53.348.6 20 57.7 55.2 21 46.9 48.0 22 48.0 44.0 23 46.5 46.5 24 51.4 53.3 2555.0 49.7 26 49.0 46.4 27 48.2 47.7 28 51.3 53.0 29 53.8 51.9 30 48.948.2 31 44.7 41.5 32 46.7 49.3 33 45.1 50.2 34 51.0 45.0 35 52.4 43.2 3649.0 48.7 37 54.0 53.6 38 51.4 50.0 39 51.6 49.9 40 45.3 49.8 41 43.946.5 42 51.6 52.7 43 54.7 49.1 44 46.2 49.8 45 49.8 49.0 46 56.3 51.3 4751.2 53.2 48 52.2 52.2 49 48.3 49.0 50 46.9 43.5 51 53.6 49.9 52 51.750.4 53 47.4 47.0 54 45.8 44.4 55 44.4 41.3 56 47.4 44.0 57 46.5 50.1 5857.1 53.3 59 53.7 53.9 60 56.6 52.1 61 41.3 48.6 62 38.9 45.4 63 42.548.3 64 45.6 38.8 65 51.3 49.2 66 50.6 49.2 67 48.5 46.6 68 38.6 43.0 6952.0 54.4 70 51.3 50.7

 

TABLE 35 Membrane Potential difference Potential difference No. beforeimmersion after immersion Present invention  71 43.2 48.2  72 44.4 48.0 73 46.9 52.3  74 40.5 53.6  75 45.3 50.0  76 40.8 43.2  77 49.6 45.3 78 43.1 38.1  79 46.5 50.2  80 54.4 55.3  84 48.8 40.5  88 56.3 53.8 92 47.6 45.5  94 54.1 56.0  98 52.0 56.3 100 48.9 50.5 105 56.9 54.3110 52.1 55.7 115 45.9 54.8 120 56.0 56.1 125 49.7 45.3 130 56.6 54.8135 47.8 51.3 140 55.4 58.0 145 49.7 53.1 150 54.6 57.6 155 57.2 53.7160 52.9 57.4 165 56.9 51.3 170 54.8 49.9 180 50.6 51.3 190 40.8 48.5200 57.0 54.9 205 48.3 51.2 210 54.7 48.0 220 48.5 50.9 ComparativeExamples Comparative 10.6  5.0 Membrane 1 Comparative 50.4 49.9 Membrane2 Comparative 57.9 55.5 Membrane 3 Comparative 56.3 51.7 Membrane 4

 

What is claimed is:
 1. A membrane sensitive to bicarbonate ioncomprising a polymer membrane which contains an onium salt structuralunit (A) and an aromatic boric diester structural unit (B) of theformula

  wherein Ar is an aromatic carbocyclic group which may optionally haveone or more substituents, either in the form of low-molecular-weightcompounds dispersed in the polymer or in a form introduced into apolymer molecule.
 2. The membrane sensitive to bicarbonate ion asclaimed in claim 1 wherein the polymer membrane contains the onium saltstructural unit (A) in the form of an onium salt compound selected fromthe group consisting of a quaternary ammonium salt, a pyridinium salt, aphosphonium salt, a sulfonium salt, an oxinium salt and an arsoniumsalt.
 3. The membrane sensitive to bicarbonate ion as claimed in claim 2wherein the onium salt compound is an onium salt compound selected fromthe group consisting of compounds of the following formulae (1), (13),(14) and (15):

  in which R¹ to R¹⁷ are each independently a hydrogen atom or anorganic group, and A⁻ is an anion.
 4. The membrane sensitive tobicarbonate ion as claimed in claim 3 wherein the organic group isrepresented by the following formula (2a), (2b) or (2c):

  in which A′ is a monovalent aliphatic hydrocarbon radical that mayhave an ether linkage, or a monovalent aromatic hydrocarbon radical thatmay have an ether linkage; A″ is a divalent aliphatic hydrocarbonradical that may have an ether linkage, or a divalent aromatichydrocarbon radical that may have an ether linkage, Y′ is a hydrogenatom or —R′—X′—A′, B′ is —N<, —CH< or

  is a divalent or trivalent aliphatic hydrocarbon radical or aromatichydrocarbon radical, X′ is —O—, —CO—, —COO— or —CONH—; i, j, k, l, m andn are each 0 or 1; when a plurality of R′ radicals are present in oneorganic group, the plurality of R′ radicals may be the same ordifferent; and the same shall apply to X′ and A′.
 5. The membranesensitive to bicarbonate ion as claimed in claim 3 wherein the oniumsalt compound is a quaternary ammonium salt of formula (1).
 6. Themembrane sensitive to bicarbonate ion as claimed in claim 5 wherein thequaternary ammonium salt is a quaternary ammonium salt selected from thegroup consisting of compounds of the following formulae (11a) and (11b):

  in which R¹ to R³ are each independently a hydrogen atom or an organicgroup, A⁻ is an anion, R^(3′) and R^(4′) are each independently adivalent organic group, X″ is a linking group such as

  is an m valent residue obtained by removing m groups or atoms from apolymer backbone,

  are each independently a monovalent moiety obtained by removing onegroup or atom from a polymer backbone, m is an integer of 1 or greater,and n is 0 or
 1. 7. The membrane sensitive to bicarbonate ion as claimedin claim 1 wherein the polymer membrane contains the aromatic boricdiester structural unit (B) derived from an aromatic boric diestercompound of the following formula (16):

  in which X¹ and X² are each independently an organic group, or X¹ andX² are combined with the atoms adjacent thereto so as to form a ringstructure, Ar′ is an aromatic hydrocarbon radical, Z is a hydrogen atomor an organic group, and s is an integer of 1 or greater.
 8. Themembrane sensitive to bicarbonate ion as claimed in claim 7 wherein thearomatic boric diester compound is a compound of the following formula(17):

  in which X is a polymerizable unsaturated group-containing divalentorganic group having two or more carbon atoms.
 9. The membrane sensitiveto bicarbonate ion as claimed in claim 7 wherein the combined X¹ and X²are represented by the following formula (19a) or (19b):

  in which M₁ to M₆ are each independently a hydrogen atom or an organicgroup.
 10. The membrane sensitive to bicarbonate ion as claimed in claim1 wherein the aromatic boric diester is a polymer consisting ofrepeating units of the structural unit (B) is represented by followingformula (18):

  in which Y is a group derived from a compound having a groupcopolymerizable with a polymerizable unsaturated group, X is atetravalent organic group having two or more carbon atoms, Ar′ is anaromatic hydrocarbon radical, Z is a hydrogen atom or an organic group,and s is an integer of 1 or greater.
 11. The membrane sensitive tobicarbonate ion as claimed in claim 7 wherein the aromatic boric diestercompound is selected from the group consisting of compounds of thefollowing formulae (22a) and (22b):

  in which M₁′ to M₆′ are independently a hydrogen atom, a methyl group,or a group derived from a polymer, Ar′ is an aromatic hydrocarbonradical, Z is an aliphatic hydrocarbon radical of 1 to 72 carbon atomsor a group comprising two aliphatic hydrocarbon radicals joined to eachother by means of —O—, —CO— or —COO—.
 12. The membrane sensitive tobicarbonate ion as claimed in claim 1 wherein the onium salt structuralunit (A) and the aromatic boric diester structural unit (B) arecontained in the form of an aromatic boric diester compound selectedfrom the group consisting of compounds of the following formulae (23),(24) and (25):

  in which at least one of L₁ to L₅ is a branched or straight-chainalkyl group of 1 to 72 carbon atoms that may have —O—, —CO—, —COO—,—CONH—, —CON< or —N═CH—, and the others are hydrogen atoms; L₆ is agroup containing a quaternary ammonium salt group; L₇ is a divalentorganic group of 1 to 8 carbon atoms; L₈ is a hydrogen atom or an alkylgroup of 1 to 3 carbon atoms; m is 0 or 1; and 0<x<1.
 13. The membranesensitive to bicarbonate ion as claimed in claim 1 wherein the polymermembrane contains the onium salt structural unit (A) and the aromaticboric diester structural unit (13) in such proportions that the molarratio of (B) to (A) is in the range of 0.1 to 100,000.
 14. The membranesensitive to bicarbonate ion as claimed in claim 1 wherein the polymermembrane contains a polymer matrix having a membrane-forming ability.15. The membrane sensitive to bicarbonate ion as claimed in claim 1wherein the polymer membrane further contains a fat-soluble anion salt.16. The membrane sensitive to bicarbonate ion as claimed in claim 15wherein the ratio of the number of moles of the fat-soluble anion saltto the number of moles of the onium salt compound is in the range of 0.1to 0.7.
 17. The composition sensitive to bicarbonate ion comprising anonium salt compound and an aromatic boric diester compound.
 18. Thecomposition as claimed in claim 17 wherein the onium salt compound is anonium salt compound selected from the group consisting of compounds ofthe following formulae (1), (13), (14) and (15):

  in which R¹ to R¹⁷ are each independently a hydrogen atom or anorganic group, and A⁻ is an anion.
 19. The composition as claimed inclaim 18 wherein the aromatic boric diester compound is an aromaticboric diester compound of the following formula (16):

  in which X¹ and X² are each independently an organic group, or X¹ andX² are combined with the atoms adjacent thereto so as to form a ringstructure, Ar′ is an aromatic hydrocarbon radical, Z is a hydrogen atomor an organic group, and s is an integer of 1 or greater.
 20. Thebicarbonate ion-selective electrode constructed by using a membranesensitive to bicarbonate ion as claimed in claim
 1. 21. The bicarbonateion-selective electrode comprising a membrane sensitive to bicarbonateion as claimed in claim 1, an internal reference electrode, and aninternal electrolyte or ionic conductive substance interposedtherebetween.
 22. An aromatic boric diester compound represented by thefollowing formula (23), (24) or (25):

  which at least one of L₁ to L₅ is a branched or straight-chain alkylgroup of 1 to 72 carbon atoms that may have —O—, —CO—, —COO—, —CONH—,—CON< or —N═CH—, and the others are hydrogen atoms; L₆ is a groupcontaining a quarternary ammonium salt group; L₇ is a divalent organicgroup of 1 to 8 carbon atoms; L₈ is a hydrogen atom or an alkyl group of1 to 3 carbon atoms; m is 0 or 1; and 0<x<1.